Achieving a low-resistance and highly stable connection between high-temperature electrodes and thermoelectric legs is a major challenge in module fabrication. Herein, we propose a method of co-sintering p-type and n-type PbTe materials with barrier layer materials, achieving a non-destructive connection of U-shaped p-n thermoelectric legs. This approach omits the metal electrode layer, effectively reducing the interfacial resistance and thermal stress. In the eight pairs of PbTe modules fabricated using this method, the total interfacial resistance accounts for only 0.6% of the internal resistance. Consequently, a high output power of 1.41 W and similar to 9.1% conversion efficiency are achieved with the temperature difference of 550 K. The module is operated for 50 thermal cycles between hot-side temperatures of 593 K and 793 K, with no significant degradation. This work demonstrates that thermoelectric modules constructed using the co-sintering method exhibit high output performance and reliability, representing a novel fabrication approach for producing high-quality thermoelectric modules.

High-performance flexible Bi 2 Te 3 -based thin films carry significant promise for future portable and wearable thermoelectric devices. In this study, a series of Bi[Formula: see text]Sb[Formula: see text]Te 3 thin films were deposited on polyimide substrates under different RF magnetron sputtering powers from 60 W to 140 W. The crystallinity, (00[Formula: see text]) preferential orientation and atomic composition can be effectively modulated by varying the sputtering power. Benefiting from the synchronous enhancements of the electrical conductivity (mostly due to the enhanced carrier mobility) and Seebeck coefficient, the film deposited under the sputtering power 100 W presents the best PF of 12.86 [Formula: see text]W cm[Formula: see text] K[Formula: see text] at 360 K and the highest average PF of 11.25 [Formula: see text]W cm[Formula: see text] K[Formula: see text] in the temperature range of 300–560 K, which are much better than those of the films deposited under other sputtering powers.

The influence of argon working pressure during magnetron sputtering on thermoelectric properties has been investigated on p-type Bi0.5Sb1.5Te3 flexible films deposited at various working pressures in the range from 2 to 5 Pa. The microstructure and orientations, atomic compositions, and carrier concentration could be regulated by adjusting the working pressure, due to the size-dependent inhibition of the deposition of the sputtered Bi, Sb, and Te atoms from argon ions. Profiting from the occurrence of the (006) orientation, the nearest stoichiometric ratio, the highest carrier concentration and mobility, and the quantum confinement effect, the film deposited at 4 Pa displays the maximum power factor of 1095 μW m−1 K−2 at 360 K. These results suggest that the electrical transport properties of the sputtered flexible thermoelectric thin films can be synergistically optimized by selecting an appropriate working pressure.

The critical current I c of single crystals of the iron pnictide superconductor BaFe2(As 1 - x P x )2 has been studied through measurements of magnetic hysteresis cycles. We show that the introduction of micrometer-scale irregularities on the surface significantly increases I c , primarily near the irreversibility magnetic field H irr . The observed increase can be attributed to a non-dissipative surface current that arises from the collective bending of the vortex lattice at the sample surface, enabled by the surface irregularities. This mechanism, which is not pinning in the proper sense, has previously been studied in clean, low- T c , metallic superconductors, but had not been investigated in Fe-based superconductors. The observed increase in I c is consistent with a theoretical estimate based on the Mathieu-Simon continuum theory of the vortex state.

We use elastic and inelastic neutron scattering (INS) to study the antiferromagnetic (AF) phase transitions and spin excitations in the two-dimensional (2D) zig-zag antiferromagnet FePSe_3. By determining the magnetic order parameter across the AF phase transition, we conclude that the AF phase transition in FePSe_3 is first-order in nature. In addition, our INS measurements reveal that the spin waves in the AF ordered state have a large easy-axis magnetic anisotropy gap, consistent with an Ising Hamiltonian, and possible biquadratic magnetic exchange interactions. On warming across T_N, we find that dispersive spin excitations associated with three-fold rotational symmetric AF fluctuations change into FM spin fluctuations above T_N. These results suggest that the first-order AF phase transition in FePSe_3 may arise from the competition between C_3 symmetric AF and C_1 symmetric FM spin fluctuations around T_N, in place of a conventional second-order AF phase transition.

The thermoelectric performance of p-type PbTe was found to be superior to that of n-type PbTe, mainly owing to the successful band engineering of the p-type materials.

An experimental determination of electronic phase diagrams of high-transition temperature (high-T_c) superconductors forms the basis for a microscopic understanding of unconventional superconductivity. For most high-T_c superconductors, the electronic phase diagrams are established through partial chemical substitution, which also induces lattice disorder. Here we show that symmetry-specific uniaxial strain can be used to study electronic phases in iron-based superconductors, composed of two-dimensional nearly square iron lattice planed separated by other elements. By applying tunable uniaxial strain along different high symmetry directions and carrying out transport measurements, we establish strain-tuning dependent electronic nematicity, antiferromagnetic (AF) order, and superconductivity of BaFe_2(As_1-xP_x)_2 superconductor. We find that uniaxial strain along the nearest Fe-Fe direction can dramatically tune the AF order and superconductivity, producing an electronic phase diagram clearly different from the chemical substitution-induced one. Our results thus establish strain tuning as a way to study the intertwined orders in correlated electron materials without using chemical substitution.

Entropy engineering is aneffective scheme to reduce the thermal conductivity of thermoelectric materials, but it inevitably deteriorates the carrier mobility. Here, we report the optimization of thermoelectric performance of PbTe by combining entropy engineering and nanoprecipitates. In the continuously tuned compounds of Pb0.98Na0.02Te(1-2x)SxSex, we show that the x = 0.05 sample exhibits an exceptionally low thermal conductivity relative to its configuration entropy. By introducing Mn doping, the produced temperature-dependent nanoprecipitates of MnSe cause the high-temperature thermal conductivity to be further reduced. A very low lattice thermal conductivity of 0.38 W m(-1) K-1 is achieved at 825 K. Meanwhile, the carrier mobility of the samples is only slightly influenced, owing to the well-controlled configuration entropy and the size of nanoprecipitates. Finally, a high peak zT of similar to 2.1 at 825 K is obtained in the Pb0.9Na0.04Mn0.06Te0.9S0.05Se0.05 alloy.

Selective carrier energy filtering effect is an important strategy to promote the power factor of a thermoelectrical materials, which requires an appropriate potential barrier and coherent interfaces between the secondary phase and the host matrix. Although the energy filtering effect has been realized in various bulk systems, its efficiency in promoting their thermoelectric performance is limited. Herein, simultaneously increased electrical conduc-tivity and Seebeck coefficient are investigated in Ag-doped Bi0.5Sb1.5Te3 films, leading to an increasement of the power factor up to 700%. Microstructure analysis reveals that the thin films prepared from magnetron sputtering consist of highly uniform nanocrystal domains, which construct coherent interfaces somewhere. Moreover, the local Ag doping might depress the Fermi level, providing the possibility to form a suitable potential barrier between the adjacent nanograins. This study suggests a facile method to significantly enhance the thermoelectric performance via energy filtering effect in high quality thin films.

Topological phonons and magnons potentially enable low-loss, quantum coherent, and chiral transport of information and energy at the atomic scale. Van der Waals magnetic materials are promising to realize such states due to their recently discovered strong interactions among the electronic, spin, and lattice degrees of freedom. Here, we report the first observation of coherent hybridization of magnons and phonons in monolayer antiferromagnet FePSe3 by cavity-enhanced magneto-Raman spectroscopy. The robust magnon-phonon cooperativity in the 2D limit occurs even in zero magnetic field, which enables nontrivial band inversion between longitudinal and transverse optical phonons caused by the strong coupling with magnons. The spin and lattice symmetry theoretically guarantee magnetic-field-controlled topological phase transition, verified by nonzero Chern numbers calculated from the coupled spin-lattice model. The 2D topological magnon-phonon hybridization potentially offers a new route toward quantum phononics and magnonics with an ultrasmall footprint.

The optimal superconductivity ($T_c \approx 30 $ K) in BaFe$_2$(As$_{1-x}$P$_x$)$_2$ can be reached when the coupled antiferromagnetic (AF) order ($T_N$) and orthorhombic lattice distortion ($T_s$) are suppressed to zero temperature with increasing of P concentration or hydrostatic pressure. Here we use transport and neutron scattering to study the $c$-axis pressure effects on electronic phases in underdoped BaFe$_2$(As$_{0.72}$P$_{0.28}$)$_2$, which has $T_N = T_s\approx 40$ K and $T_c \approx $ 28 K at zero pressure. With increasing $c$-axis pressure, $T_N$ and $T_s$ are slightly enhanced around $P_c \sim 20 $ MPa. Upon further increasing pressure, AF order is gradually suppressed to zero, while $T_c$ is enhanced to 30 K. Our results reveal the importance of magnetoelastic couplings in BaFe$_2$(As$_{1-x}$P$_x$)$_2$, suggesting that the $c$-axis pressure can be used as a tuning parameter to manipulate the electronic phases in iron pnictides.

We have systematically studied physical properties of Ba(Fe_{0.97}Cr_{0.03})_{2}(As_{1-x}P_{x})_{2}, where superconductivity in BaFe_{2}(As_{1-x}P_{x})_{2} is fully suppressed by just 3% of Cr substitution of Fe. A quantum critical point is revealed at x∼0.42, where non-Fermi-liquid behaviors similar to those in BaFe_{2}(As_{1-x}P_{x})_{2} are observed. Neutron diffraction and inelastic neutron scattering measurements suggest that the quantum critical point is associated with the antiferromagnetic order, which is not of conventional spin-density-wave type as evidenced by the ω/T scaling of spin excitations. On the other hand, no divergence of low-temperature nematic susceptibility is observed when x is decreased to 0.42 from higher doping level, demonstrating that there are no nematic quantum critical fluctuations. Our results suggest that non-Fermi-liquid behaviors in iron-based superconductors can be solely resulted from the antiferromagnetic quantum critical fluctuations, which cast doubts on the role of nematic fluctuations played in the normal-state properties in iron-based superconductors.

in BaðFe0.97Cr0.03Þ2ðAs1− xPxÞ2 Wenliang Zhang, Yuan Wei, Tao Xie, Zhaoyu Liu, Dongliang Gong, Xiaoyan Ma, Ding Hu, Petr Čermák, Astrid Schneidewind, Gregory Tucker, Siqin Meng, Zita Huesges, Zhilun Lu, Jianming Song, Wei Luo, Liangcai Xu, Zengwei Zhu, Xunqing Yin, Hai-Feng Li, Yi-feng Yang, Huiqian Luo, and Shiliang Li 1 Beijing National Laboratory for Condensed Matter Physics, Institute of Physics,

We used transport and inelastic neutron scattering to study the optimally phosphorus-doped BaFe$_2$(As$_{0.7}$P$_{0.3}$)$_2$ superconductor ($T_c = 30$ K). In the normal state, we find that the previously reported linear temperature dependence of the resistivity below room temperature extends to $\sim$ 500 K. Our analysis of the temperature and energy ($E=\hbar\omega$) dependence of spin dynamical susceptibility at the antiferromagnetic (AF) ordering wave vector $\chi^{\prime\prime}({\bf Q}_{\rm AF},\omega)$ reveal an $\omega / T$ scaling within $1.1

Superconductivity in BaFe 2 (As 1− x P x ) 2 iron pnictides emerges when its in-plane two-dimensional (2D) orthorhombic lattice distortion associated with nematic phase at T s and three-dimensional (3D) collinear antiferromagnetic order at T N ( T s = T N ) are gradually suppressed with increasing x , reaching optimal superconductivity around x = 0.30 with T c ≈ 30 K. Here we show that a moderate uniaxial pressure along the c -axis in BaFe 2 (As 0.70 P 0.30 ) 2 spontaneously induces a 3D collinear antiferromagnetic order with T N = T s > 30 K, while only slightly suppresses T c . Although a ~ 400 MPa pressure compresses the c -axis lattice while expanding the in-plane lattice and increasing the nearest-neighbor Fe–Fe distance, it barely changes the average iron-pnictogen height in BaFe 2 (As 0.70 P 0.30 ) 2 . Therefore, the pressure-induced antiferromagnetic order must arise from a strong in-plane magnetoelastic coupling, suggesting that the 2D nematic phase is a competing state with superconductivity.

We use inelastic neutron scattering to study acoustic phonons and spin excitations in single crystals of NaFeAs, a parent compound of iron pnictide superconductors. NaFeAs exhibits a tetragonal-to-orthorhombic structural transition at $T_s\approx 58$ K and a collinear antiferromagnetic (AF) order at $T_N\approx 45$ K. While longitudinal and out-of-plane transverse acoustic phonons behave as expected, the in-plane transverse acoustic phonons reveal considerable softening on cooling to $T_s$, and then harden on approaching $T_N$ before saturating below $T_N$. In addition, we find that spin-spin correlation lengths of low-energy magnetic excitations within the FeAs layer and along the $c$-axis increase dramatically below $T_s$, and show weak anomaly across $T_N$. These results suggest that the electronic nematic phase present in the paramagnetic tetragonal phase is closely associated with dynamic spin-lattice coupling, possibly arising from the one-phonon-two-magnon mechanism.