High-performance non-Fermi-liquid metallic thermoelectric materials

Searching for high-performance thermoelectric(TE)materials in the paradigm of narrow-bandgap semiconductors is hampered by a bottleneck.Here we report on the discovery of metallic compounds,TiFe_(x)Cu_(2x−1)Sb and TiFe1.33Sb,showing the thermopower exceeding many TE semiconductors and the dimensionless figure of merits zTs comparable with the state-of-the-art TE materials.A quasi-linear temperature(T)dependent electrical resistivity in 2–700 K and the logarithmic T-dependent electronic specific heat at low temperature coexist with the high thermopower,highlighting the strong intercoupling of the non-Fermi-liquid(NFL)quantum critical behavior of electrons with TE transports.Electronic structure analysis reveals a competition between the antiferromagnetic(AFM)ordering and Kondo-like spin compensation as well as a parallel two-channel Kondo effect.The T-dependent magnetic susceptibility agrees with the quantum critical scenario of strong local correlation.Our work demonstrates the correlation among high TE performance,NFL quantum criticality,and magnetic fluctuation,which opens up directions for future research.

Combined subsampling and analytical integration for efficient large-scale GW calculations for 2D systems

Accurate and efficient predictions of the quasiparticle properties of complex materials remain a major challenge due to the convergence issue and the unfavorable scaling of the computational cost with respect to the system size.Quasiparticle GW calculations for two-dimensional(2D)materials are especially difficult.The unusual analytical behaviors of the dielectric screening and the electron self-energy of 2D materials make the conventional Brillouin zone(BZ)integration approach rather inefficient and require an extremely dense k-grid to properly converge the calculated quasiparticle energies.In this work,we present a combined nonuniform subsampling and analytical integration method that can drastically improve the efficiency of the BZ integration in 2D GW calculations.

Prediction of protected band edge states and dielectric tunable quasiparticle and excitonic properties of monolayer MoSi_(2)N_(4)

The electronic structure of two-dimensional(2D)materials are inherently prone to environmental perturbations,which may pose significant challenges to their applications in electronic or optoelectronic devices.A 2D material couples with its environment through two mechanisms:local chemical coupling and nonlocal dielectric screening effects.The local chemical coupling is often difficult to predict or control experimentally.Nonlocal dielectric screening,on the other hand,can be tuned by choosing the substrates or layer thickness in a controllable manner.Therefore,a compelling 2D electronic material should offer band edge states that are robust against local chemical coupling effects.Here it is demonstrated that the recently synthesized MoSi_(2)N_(4)is an ideal 2D semiconductor with robust band edge states protected from capricious environmental chemical coupling effects.Detailed many-body perturbation theory calculations are carried out to illustrate how the band edge states of MoSi_(2)N_(4)are shielded from the direct chemical coupling effects,but its quasiparticle and excitonic properties can be modulated through the nonlocal dielectric screening effects.This unique property,together with the moderate band gap and the thermodynamic and mechanical stability of this material,paves the way for a range of applications of MoSi_(2)N_(4)in areas including energy,2D electronics,and optoelectronics.

MatHub-2d:二维材料输运数据库及其高迁移率二维半导体材料高通量筛选应用

近些年来二维材料因其独特的物理化学性质引起了广泛关注.载流子迁移率是材料在电子设备应用中最重要的特性之一.在本文中,我们介绍了如何通过高通量计算筛选来发现高迁移率二维半导体材料.基于最近开发的MatHub-2d数据库(包含约1900个二维材料的结构信息及其第一性原理计算结果),以带隙、磁性、弹性模量和形变势作为搜索标准,通过初步筛选,得到133个候选者.对这些体系,我们使用形变势方法和玻尔兹曼输运理论预测了迁移率.最终,我们预测19种二维材料在室温下(300 K)具有高迁移率(>10^(3)cm^(-2)V^(-1)s^(-1))和良好的稳定性.这些材料高迁移率的来源主要是较小的形变势常数、较大的弹性模量,以及较小的有效质量.其中有两种类型的化合物值得关注,BX(X=P,As,Sb)和ZO_(2)(Z=Ge,Sn,Pb),它们具有面内各向同性高迁移率.BX中“flower-like”化学键有利于p型和n型电输运,而Z-O反键态是ZO_(2)型二维材料良好电子传导的原因.除了这些二维材料,Si_(2)P_(2)、Ga_(2)O_(2)、Ge_(2)N_(2)等同样也表现出高的电子迁移率.这些高迁移率二维材料在新型半导体电子器件中具有潜在的应用前景.

Violation of the T^(−1) Relationship in the Lattice Thermal Conductivity of Mg_(3)Sb_(2) with Locally Asymmetric Vibrations

Most crystalline materials follow the guidelines of T^(-1) temperature-dependent lattice thermal conductivity(κ_(L))at elevated temperatures.Here,we observe a weak temperature dependence ofκL in Mg_(3)Sb_(2),T^(-0:48) from theory and T-0:57 from measurements,based on a comprehensive study combining ab initio molecular dynamics calculations and experimental measurements on single crystal Mg_(3)Sb_(2).These results can be understood in terms of the so-called“phonon renormalization”effects due to the strong temperature dependence of the interatomic force constants(IFCs).The increasing temperature leads to the frequency upshifting for those low-frequency phonons dominating heat transport,and more importantly,the phononphonon interactions are weakened.In-depth analysis reveals that the phenomenon is closely related to the temperature-induced asymmetric movements of Mg atoms within MgSb_(4) tetrahedron.With increasing temperature,these Mg atoms tend to locate at the areas with relatively low force in the force profile,leading to reduced effective 3^(rd)-order IFCs.The locally asymmetrical atomic movements at elevated temperatures can be further treated as an indicator of temperature-induced variations of IFCs and thus relatively strong phonon renormalization.The present work sheds light on the fundamental origins of anomalous temperature dependence of κ_(L) in thermoelectrics.