Owing to their extraordinary photophysical properties, organometal halide perovskites are emerging as a new material class for X-ray detection. However, the existence of toxic lead makes their commercialization questionable and should readily be replaced. Accordingly, several lead alternatives have been introduced into the framework of conventional perovskites, resulting in various new perovskite dimensionalities. Among these, Pb-free lower dimensional perovskites (LPVKs) not only show promising X-ray detecting properties due to their higher ionic migration energy, wider and tunable energy bandgap, smaller dark currents, and structural versatility but also exhibit extended environmental stability. Herein, first, the structural organization of the PVKs (including LPVKs) is summarized. In the context of X-ray detectors (XDs), the outstanding properties of the LPVKs and active layer synthesis routes are elaborated afterward. Subsequently, their applications in direct XDs are extensively discussed and the device performance, in terms of the synthesis method, device architecture, active layer size, figure of merits, and device stability are tabulated. Finally, the review is concluded with an in-depth outlook, thoroughly exploring the present challenges to LPVKs XDs, proposing innovative solutions, and future directions. This review provides valuable insights into optimizing non-toxic Pb-free perovskite XDs, paving the way for future advancements in the field. Organometal halide perovskites with exceptional properties are promising for X-ray detection, yet the presence of toxic lead (Pb) raises concerns. This review explores Pb-free alternatives, including lower dimensional perovskites, highlighting their advantageous attributes for X-ray detection. It covers synthesis, applications, and challenges, offering insights for enhancing non-toxic, lower-dimensional perovskites X-ray detectors.image

Al 2 O 3 /SrTiO 3 heterostructures have attracted wide attention because of high electron mobility at cryogenic temperatures. But very low room temperature mobility (typically less than 12 cm 2 V −1 s −1 ) limits its potential application. Here, the Al 2 O 3 /SrTiO 3 heterostructures are successfully prepared by the low-cost magnetron sputtering. We observed that room temperature mobility is gradually enhanced on increasing electron concentration, and a maximum of 41.1 cm 2 V −1 s −1 is obtained. This can be attributed to the high electron concentration due to the longitudinal optical phonon scattering. Our findings not only offer a route to improve room temperature mobility of the SrTiO 3 -based heterostructures but also provide a new experimental method for fabricating Al 2 O 3 /SrTiO 3 heterostructures.

The origin of the intermediate anomalous metallic state in two-dimensional superconductor materials remains enigmatic. In the present paper, we observe such a state in a series of $\sim$9.0 nm thick Ta$_x$(SiO$_2$)$_{1-x}$ ($x$ being the volume fraction of Ta) nanogranular films. At zero field, the $x$ $\gtrsim$ 0.75 films undergo a Berezinskii-Kosterlitz-Thouless transition as transform from normal to superconducing states upon cooling. For the $x$ $\lesssim$ 0.71 films, the resistance increases with decreasing temperature from 2 K down to 40 mK. A normal state to anomalous metallic state transition is observed in the $x$ $\simeq$ 0.73 film, i.e., near the transition temperature, the resistance of the film decreases sharply upon cooling as if the system would cross over to superconducting state, but then saturates to a value far less than that in normal state. When a small magnetic field perpendicular to the film plane is applied, the anomalous metallic state occurs in the $x$ $\gtrsim$ 0.75 films. It is found that both disorder and magnetic field can induce the transition from superconductor to anomalous metal and their influences on the transition are similar. For the the magnetic field induced case, we find the sheet resistance $R_{\square}(T,H)$ ($T$ and $H$ being the temperature and the magnitude of magnetic field) data near the crossover from the anomalous metal to superconductor and in the vicinity of the anomalous metal to insulator transition, respectively, obey unique scaling laws deduced from the Bose-metal model. Our results strongly suggest that the anomalous metallic state in the Ta$_x$(SiO$_2$)$_{1-x}$ granular films is bosonic and dynamical gauge field fluctuation resulting from superconducting quantum fluctuations plays a key role in its formation.

In recent years, the research on topological materials, including topological insulator and topological semimetal, has received a lot of attention in condensed matter physics. HgCdTe, widely used in infrared detection, also holds huge potential in this field. It has been reported that the strained thin Hg0.865Cd0.135Te can realize topological insulator phase by using a CdZnTe substrate. However, the stress caused by changing substrate has great limitations. For example, the stress cannot be changed once the sample has been grown. Hence, we try to use a piezoceramics (PZT) instead to implement the stress and control the properties of HgCdTe. The main purpose of our experiment is to verify its validity. As is well known, the band structure of Hg1–xCdxTe can be precisely controlled by changing the content of Cd. When x lies between 0 and 0.165, HgCdTe features an inverted band structure, which is the premise of realizing topological phase. In this work, an inversion layer is induced on a single crystal grown HgCdTe bulk material by anodic oxidation, whose content of Cd is confirmed to be 0.149 by using XRD. Then the sample is thinned and attached to a PZT, which the tuning of stress is realized by applying a voltage to. Ohmic contacts are realized by indium in van der Pauw configuration. All measurements are carried out by using an Oxford Instruments 4He cryostat with magnetic field applied perpendicularly to the sample plane. At 1.5 K and zero voltage, an evident SdH oscillation is observed. By fitting the linear relationship between filling factor and the reciprocal of magnetic field, the concentration is obtained to be \begin{document}${n_{\rm{s}}} = 1.25 \times {10^{16}}\;{{\rm{m}}^{ - 2}}$\end{document}. Subsequently, we scan the voltage from 200 V to –200 V continuously in different magnetic fields. Two phenomena with different characteristics are observed. It is found that the resistance changes linearly with stress at zero field while an SdH oscillation-like behavior occurs at high field. We attribute such a difference to the existence of two conductive channels: one is the bulk material and the other is the two-dimensional electron gas. It is also noteworthy that the topological phase in our sample cannot be determined because the quantum Hall conductance is polluted by the conductance of bulk material. In conclusion, our results show that it is an effective way to use the PZT to tune the stress and this method can also be applied to the research of other materials.

The spin-orbit coupling interaction,Zeeman effect and interface microroughness effect in an HgCdTe inversion layer were investigated by experimental measurement. Theoretical models were used to analyze the weak antilocalization (WAL)at different temperatures and in different in-plane magnetic fields. It is found that both the Zeeman effect and the interface microroughness effect will suppress the WAL. And the interface microroughness effect takes effect by facilitating a weak localization in the normal direction of the two-dimensional electron gas (2DEG) plane. With the increasing magnetic field,the interface microroughness induced WL will be suppressed first and then the WAL will be suppressed by Zeeman effect. What's more,the analysis of parameters tau/tau(phi) and vertical bar m*, g(3)*vertical bar| indicates that the Zeeman effect's suppression on WAL does not depend on temperature.

Anisotropy in electronic structures may ignite intriguing anisotropic optical responses, as has been well demonstrated in various systems including superconductors, semiconductors, and even topological Weyl semimetals. Meanwhile, it is well established in metal optics that the metal reflectance declines from one to zero when the photon frequency is above the plasma frequency omega(p), behaving as a plasma mirror. However, the exploration of anisotropic plasma mirrors and corresponding applications remains elusive, especially at room temperature. Here, we discover a pronounced anisotropic plasma reflectance edge in the type-II Weyl semimetal WP2, with an anisotropy ratio of omega(p) up to 1.5. Such anisotropic plasma mirror behavior and its robustness against temperature promise optical device applications over a wide temperature range. For example, the high sensitivity of polarization-resolved plasma reflectance edge renders WP2 an inherent polarization detector. We further achieve a room-temperature WP2-based optical switch, effectively controlled by simply tuning the light polarization. These findings extend the frontiers of metal optics as a discipline and promise the design of multifunctional devices combining both topological and optical features.

The infrared (IR) reflectivity of the cubic metal oxides MgO, MnO, and NiO has been measured at room temperature using the technique of oblique incidence. The use of this technique at three angles of incidence provides multiple sets of spectra (including both s- and p-polarizations) to analyze when compared to the standard normal incidence case, which has been used extensively in the past for these compounds. It is shown that the transverse optic (TO) and longitudinal optic (LO) mode phonon parameters can be determined with greater accuracy by using the factorized model for the fits, as compared with the popular classical model used previously, and by fitting the derivative of the reflectivity. Our results for the phonon mode parameters are similar to those found earlier, as could be expected, but are generally more precise. An analysis of the difference in frequency of the TO mode in antiferromagnetic NiO at room temperature for the two polarizations of reflected light revealed a TO mode splitting of about 4 cm(-1), with the p-polarized light TO mode having the higher frequency: This small splitting is in agreement with theoretical predictions. This more precise IR method for revealing the phonon mode behavior in such magnetically ordered cubic metal oxides, which are prototypes of strongly correlated electronic systems and have been found to be Mott-Hubbard insulators, may be readily applied to any similar antiferromagnetic system.

Here we report the observation of the anomalous field effect, manifested as apparent electric hysteresis and decreasing resistance in the negative gate bias region in an Al0.087Ga0.913N/GaN heterostructure quantum well at low temperature. Together with this, slow relaxation of resistivity was observed. Magnetotransport measurements were carried out to determine the origin of such phenomena. The results show that the origin of electric hysteresis and slow relaxation is the capture and release of electrons by traps located in regions of the device structure outside of the conducting 2DEG channel. Besides, the existence of slow dynamics at only low temperature indicates that the traps involved should be shallow impurities. As for the anomalous reduced resistance when applying negative gate bias, it should come from the increase of mobility, which is due to the dominant role of interface roughness scattering at low temperature.

This paper reports the study of the magneto-transport properties of a two-dimensional electron gas confined in inversion layers on HgCdTe with an inverted band structure. The magnetoresistance exhibits Shubnikov-de Hass oscillations, where beating patterns are observed at low magnetic field. This can be attributed to the zero-field spin splitting. By using the fast Fourier transformation of the observed beating patterns, the zero-field spin splitting energy is extracted. The extracted energy up to similar to 34 meV is obtained, which is far larger than that in inversion layers on HgCdTe with a normal band structure. This offers a route to realize a HgTe-based spintronic device that works at room temperature. Copyright (C) EPLA, 2018

Single-crystalline Bi2Se3 and Bi-2 (TexSe1-x)(3) nanowires were synthesized via Au catalytic vapor-liquid solid (VLS) growth method. Electronic properties of the surface states in individual Bi-2 (TexSe1-x)(3), (x = 0.26) nanowire were studied by low-temperature magnetotransport measurement. Weak antilocalization (WAL) effect was found, suggesting strong spin-orbit coupling in our samples. It is indicated that the bulk effect can be suppressed effectively by the Tellurium (Te) doping. By fitting the magnetoconductance curves at magnetic field up to 7 T measured at different temperatures, the extracted dephasing length l(phi) decreases from 389 nm at 1.5 K to 39 nm at 20 K, which can be well described by the power law l phi proportional to T-0.96. It can be reasonably deduced that both the electron-electron scattering and the electron-phonon scattering play important roles in the Te-doped sample.

In recent years, spintronic devices have attracted more and more attention because of their good characteristics. The spin-orbit coupling of HgCdTe is one of the most important parts in the study of narrow gap semiconductors. The magneotransport properties of the Hg0.9Cd0.1Te bulk material with an inverted band structure have been hardly reported so far. The spin-orbit coupling strength of HgCdTe is closely related to the band gap. The strength of the spin-orbit coupling increases with the width of the band gap decreasing. Thus, Hg0.9Cd0.1Te should have strong spin-orbit coupling. Meanwhile it should be one of the most suitable materials to fabricate spintronic devices. The main propose of our experiments is to prove this inference. Inside the sample, Rashba spin-orbit interaction (SOI) strongly influences the spin-splitting due to the lack of structural inversion symmetry. In other words, Rashba SOI is the main part of the zero field spin splitting △0. The band structure of Hg1-xCdxTe can be precisely tuned by changing the composition of Cd which keeps an inverted band order when 0 x Γ8 band lying below the Γ6 band (or equivalently a positive band gap) when x0.165. In this paper, the p-type HgCdTe bulk material with Cd component of 0.1 is grown by single crystal. Anodic oxidation is used to induce an inversion layer on the HgCdTe bulk, and indium is used to facilitate Ohmic contacts. The magnetoresistance is measured in the van der Pauw configuration, and the magnetic field is applied perpendicularly to the film. All measurements are carried out in an Oxford Instruments He cryogenic system. At 1.5 K and zero gate voltage, the carrier density n is 1.3×1016 m-2. Clear Shubnikov-de Haas (SdH) oscillation in ρxx and quantum Hall plateaus of Rxy are observed in the Hg0.9Cd0.1Te bulk material with an inverted band structure is investigated in magnetotransport experiment. This indicates that our sample is a good transistor. Fast Fourier transformation is used to deduce the zero-field spin-splitting △0 which is about 26.55 meV. By studying the beating patterns in SdH oscillations we find that the effective g-factor is about-11.54. Both the large zero field spin splitting and the negative effective g-factor suggest that Hg0.9Cd0.1Te has really strong spin-orbit coupling. The investigation of SOI in Hg0.9Cd0.1Te can increase our knowledge of Hg-based narrow-gap semiconductors and benefit the field of spintronics.

Spin-orbit coupling (SOC) plays a crucial role for spintronics applications. Here we present the first demonstration that the Rashba SOC at the SrTiO3-based interfaces is highly tunable by photoinduced charge doping, that is, optical gating. Such optical manipulation is nonvolatile after the removal of the illumination in contrast to conventional electrostatic gating and also erasable via a warming-cooling cycle. Moreover, the SOC evolutions tuned by illuminations with different wavelengths at various gate voltages coincide with each other in different doping regions and collectively form an upward-downward trend curve: In response to the increase of conductivity, the SOC strength first increases and then decreases, which can be attributed to the orbital hybridization of Ti 3d subbands. More strikingly, the optical manipulation is effective enough to tune the interferences of Bloch wave functions from constructive to destructive and therefore to realize a transition from weak localization to weak antilocalization. The present findings pave a way toward the exploration of photoinduced nontrivial quantum states and the design of optically controlled spintronic devices.

HgTe plates have been grown by vapor phase epitaxy on (111) SrTiO3 substrates with a preferred orientation in the (111) crystalline direction, as indicated by x-ray diffraction. Examination of the plates using the micro-Raman mapping shows that the HgTe plates exhibit unusual strain patterns: the Raman peaks from the transverse-optical and longitudinal-optical phonons for the thicker (central) parts of the HgTe plates are at the same frequency as that of the bulk HgTe, while the Raman peaks for the thinner parts of the HgTe plates, which surround the thicker parts and can hardly be seen in a scanning electron microscope, are significantly larger in frequency. The full width at half maximum is smaller in the thinner areas than in the thicker parts. Theoretical analysis shows that the HgTe plates on SrTiO3 substrates suffer from compressive stress, and this may be sufficient to induce the three-dimensional topological insulator behavior in HgTe.

We studied the suppression of the weak antilocalization (WAL) effect and the dependence of spin dynamics for a two-dimensional electron gas in the inversion layers of two different Hg 1− x Cd x Te samples in the presence of in-plane magnetic field . The WAL magnetoconductance is fitted by the Golub model to acquire the variations of phase coherence time with increasing . The effective g -factors in the form of ( is the relative effective mass) at zero magnetic field and high magnetic field are obtained by investigating the electron dephasing with varying and measuring the spin splitting of the Shubnikov-de Hass oscillations, respectively. As the obtained g -factors are in accordance with the reported results, the suppression of the WAL effect can be attributed to the competition between Zeeman splitting and spin-orbit interaction rather than to the microroughness scattering.

Localized strain accumulation and related defects strongly affect the performance of optoelectronic detectors. However, characterizing distribution of the localized strain and defects still challenges usability and spatial resolution of many measurements. In current study, the defects and surface strain accumulation of In0.83Al0.17As/In0.83Ga0.17As multilayer detectors are investigated using low-frequency atomic force acoustic microscope (AFAM) and Raman spectroscopy. With AFAM, the strain accumulation and defects can be easily identified and measured with spatial resolution as good as that of atomic force microscope (AFM).

High quality InAs0.94Sb0.06 films were grown on InAs substrates by the liquid phase epitaxy technique. The structural characteristics and cross-section morphology of InAs0.94Sb0.06 samples were investigated by high-resolution x-ray diffraction measurements and scanning electronic microscopy measurements, respectively. The refractive index and extinction coefficient spectra of InAs0.94Sb0.06 film near the energy band gap were obtained by fitting room temperature infrared spectroscopic ellipsometry with the model of dielectric function in the range of 3 000 to 6 000 nm. The energy band gap of InAs0.94Sb0.06 was 0. 308 eV, which was determined by refractive enhancement.

研究了非对称In_（0.53）Ga_（0.47）As/In_（0.52）Al_（0.48）As量子阱中二维电子气的磁输运性质,所测量的样品的径向磁阻R_（xx）的Shubinikov-de Haas振荡没有呈现出拍频的特征。通过测量样品的反弱局域效应提取了其零场自旋分裂能并通过对自旋分裂的R_（xx）双峰间距随倾斜角度θ的依赖关系的拟合提取了高场下的有效g因子。样品的Dingle plot图呈现非线性的特征,这可以归因于来自样品衬底附近的掺杂Be原子的长程势散射效应。

Magnetic metallic multilayers separated by nonmagnetic metal films are of great importance in magnetoelectronics and spintronics, due to their capacity of giving rise to giant magneto-resistance as well as the electric field control of ferromagnetism. Co/Pt multilayers are one of the typical platforms that own perpendicular magnetic anisotropy which can be tuned in various ways. Since previous investigations focus on the anomalous Hall( transverse) resistivity which characterizes the magnetization of the multilayers, much less attention has been paid to the longitudinal resistivity. In this work, we find that the longitudinal resistivity also gives rich phenomena that need further theoretical treatment. We have grown two Co/Pt multilayer structures that have different spacings between neighboring ferromagnetic layers. The one with smaller spacing shows a superparamagnetic behavior in its Hall resistivity even at a temperature as low as 1.5 K, but the longitudinal resistivity shows a well established hysteresis. The other sample shows square hysteresis in the Hall resistivity at all available temperatures up to 300 K, while the longitudinal resistivity gives no significant signals because they are mostly engulfed in the noises. The corresponding temperature dependence of the coercive field are also different. While the former gives an approximately exponential function of the temperature T, the latter can be divided to two zones, each of which can be characterized by a lnT(s) dependence, where s is not necessarily an integer. Such distinct features may be deeply related to the microstructures as well as the magnon scattering, which require further investigations.

Spin-orbit coupling (SOC) for d-electron gas can be substantially enriched compared with the sp-electron gas due to the delicate ordering of the multiple d subbands. Here, we demonstrate the nontrivial Rashba SOC effect at SrTiO3-based interfaces (LaAlO3/SrTiO3 and LaVO3/SrTiO3) directly related to the Ti 3d subband ordering via magnetotransport characterizations. Unusual k-cubic Rashba SOC contributed from the d(xz/yz) states is revealed. More strikingly, when a gate voltage is swept to tune the band filling, the SOC strength initially increases and then decreases to form a dome feature, accompanied by an apparent single- to two-carrier transition. These two concomitant effects strongly indicate that the SOC behavior is largely determined by the Ti 3d subbands regardless of the overlayer boundary conditions, with the SOC strength peaked at the d(xy)-d(xz/yz) crossings due to the band hybridization effect as predicted. The present findings offer new insights into exploration of oxide-based quantum phases and spintronic devices.

This paper investigated the magnetotransport properties of the two-dimensional electron system in an asymmetrical In0.53Ga0.47As/In0.52Al0.48As quantum well, in which the expected beatings in the Shubinikov-de Haas oscillations of the longitudinal magnetoresistance R-xx not observed. Zero-field spin splitting was extracted by measuring the weak anti-localization effect and the high field effective g-factor, g*, was extracted by fitting the tilt angle theta-dependent spacing of spin-splitted R-xx peaks. The Dingle plot is shown to be nonlinear, which can be attributed to the long-range scattering potential from the doping Be atoms near the substrate.