Colossal negative magnetoresistance in spin glass Na(Zn,Mn)Sb

We report the study of magnetic and transport properties of polycrystalline and single crystal Na(Zn,Mn)Sb,a new member of“111”type of diluted magnetic materials.The material crystallizes into Cu2Sb-type structure which is isostructural to“111”type Fe-based superconductors.With suitable carrier and spin doping,the Na(Zn,Mn)Sb establishes spin-glass ordering with freezing temperature(Tf)below 15 K.Despite lack of long-range ferromagnetic ordering,Na(Zn,Mn)Sb single crystal still shows sizeable anomalous Hall effect below Tf.Carrier concentration determined by Hall effect measurements is over 1019 cm-3.More significantly,we observe colossal negative magnetoresistance(MR≡[ρ(H)−ρ(0)]/ρ(0))of-94%in the single crystal sample.

Pressure induced insulator to metal transition in quantum spin liquid candidate NaYbS_(2)

Pressure induced insulator to metal transition followed by the appearance of superconductivity has been observed recently in inorganic quantum spin liquid candidate NaYbSe_(2).In this paper,we study the properties of isostructural compound NaYbS_(2)under pressure.It is found that the resistance of Na YbS_(2)single crystal exhibits an insulating state below 82.9 GPa,but with a drop of more than six orders of magnitude at room temperature.Then a minimum of resistance is observed at about 100.1 GPa and it moves to lower temperature with further compression.Finally,a metallic state in the whole temperature range is observed at about 130.3 GPa accompanied by a non-Fermi liquid behavior below 100 K.The insulator to metal transition,non-monotonic resistance feature and non-Fermi liquid behavior of NaYbS_(2)under pressure are similar to those of NaYbSe_(2),suggesting that these phenomena might be the universal properties in NaLnCh_(2)(Ln=rare earth,Ch=O,S,Se)system.

Superconductivity above 30 K Achieved in Dense Scandium

Superconductivity is one of most intriguing quantum phenomena,and the quest for elemental superconductors with high critical temperature(T_(c))is of great scientific significance due to their relatively simple material composition and the underlying mechanism.Here we report the experimental discovery of densely compressed scandium(Sc)becoming the first elemental superconductor with T_(c)breaking into 30 K range,which is comparable to the T_(c)values of the classic La-Ba-Cu-O or LaFeAsO superconductors.Our results show that T_(c)^(onset)of Sc increases from~3K at around 43GPa to~32K at about 283GPa(T_(c)^(zero)~31 K),which is well above liquid neon temperature.Interestingly,measured T_(c)shows no sign of saturation up to the maximum pressure achieved in our experiments,indicating that T_(c)may be even higher upon further compression.

Long-Time Magnetic Relaxation in Antiferromagnetic Topological Material EuCd_(2)As_(2)

Magnetic topological materials have attracted much attention due to the correlation between topology and magnetism.Recent studies suggest that EuCd_(2)As_(2) is an antiferromagnetic topological material.Here by carrying out thorough magnetic,electrical and thermodynamic property measurements,we discover a long-time relaxation of the magnetic susceptibility in EuCd_(2)As_(2).The(001)in-plane magnetic susceptibility at 5 K is found to continuously increase up to∼10%over the time of∼14 hours.The magnetic relaxation is anisotropic and strongly depends on the temperature and the applied magnetic field.These results will stimulate further theoretical and experimental studies to understand the origin of the relaxation process and its effect on the electronic structure and physical properties of the magnetic topological materials.

Temperature Dependence of the Electronic Structure of Ca_(3)Cu_(2)O_(4)Cl_(2) Mott Insulator

We use scanning tunneling microscopy to study the temperature evolution of electronic structure in Ca_(3)Cu_(2)O_(4)Cl_(2) parent Mott insulator of cuprates. It is found that the upper Hubbard band moves towards the Fermi energy with increasing temperature, while the charge transfer band remains basically unchanged. This leads to a reduction of the charge transfer gap size at high temperatures, and the rate of reduction is much faster than that of conventional semiconductors. Across the Neel temperature for antiferromagnetic order, there is no sudden change in the electronic structure. These results shed new light on the theoretical models about the parent Mott insulator of cuprates.

Superconductivity above 70 K observed in lutetium polyhydrides

The binary polyhydrides of heavy rare earth lutetium that shares a similar valence electron configuration to lanthanum have been experimentally discovered to be superconductive.The lutetium polyhydrides were successfully synthesized at high pressure and high temperature conditions using a diamond anvil cell in combinations with the in-situ high pressure laser heating technique.The resistance measurements as a function of temperature were performed at the same pressure of synthesis in order to study the transitions of superconductivity(SC).The superconducting transition with a maximum onset temperature(Tc)71 K was observed at pressure of 218 GPa in the experiments.The Tcdecreased to 65 K when pressure was at 181 GPa.From the evolution of SC at applied magnetic fields,the upper critical field at zero temperatureμ0Hc2(0)was obtained to be~36 T.The in-situ high pressure X-ray diffraction experiments imply that the high TcSC should arise from the Lu4H23phase with Pm3n symmetry that forms a new type of hydrogen cage framework different from those reported for previous light rare earth polyhydride superconductors.

Relationship between the parent charge transfer gap and maximum transition temperature in cuprates

One of the biggest puzzles concerning the cuprate high temperature superconductors is what determines the maximum transition temperature(Tc,max), which varies from less than 30 to above 130 K in different compounds.Despite this dramatic variation, a robust trend is that within each family, the double-layer compound always has higher Tc,maxthan the single-layer counterpart. Here we use scanning tunneling microscopy to investigate the electronic structure of four cuprate parent compounds belonging to two different families. We find that within each family, the double layer compound has a much smaller charge transfer gap size(DCT), indicating a clear anticorrelation between DCTand Tc,max. These results suggest that the charge transfer gap plays a key role in the superconducting physics of cuprates, which shed important new light on the high Tc mechanism from doped Mott insulator perspective.

莫特绝缘体母体Ca_(2)CuO_(2)Cl_(2)中的掺杂空位对诱导的原子级电子态的直接成像

使用扫描隧道显微镜研究了铜氧化物莫特绝缘体母体Ca_(2)CuO_(2)Cl_(2)中由2个空穴型掺杂空位组成的掺杂对所诱导的原子尺度电子态.随着2个掺杂空位的接近,高能的Hubbard能带的谱权重会转移到低能的能隙内电子态,形成一个平缓的峰并且展示出一个在费米能附近的V型能隙.峰的位置会在2个掺杂空位靠近到4倍晶格常数时突然下降并在之后保持不变.能隙内电子态表现出取决于2个掺杂空位相对于底层铜晶格的构型的特殊空间分布.这些结果为在母体铜氧化物中轻度空穴掺杂的低能电子态的演化提供了重要的新线索.

Superconductivity of a cuprate with compressed local octahedron

Since the historical discovery of high Tc superconductivity(HTS)of La2CuO4 in 1986[1],the superconductivity me chanism of copper oxides remains one of the biggest mysteries in the field of condensed matter physics[2-10].High-Tc cuprates crystallize into layered perovskite structure,as well as copper oxygen octahedron coordination.In octahedron symmetry,the 3d orbitals of Cu^2+with a 3d^9 configuration degenerate into two top eg and three lower t2g orbitals.

一种新型铬基砷化物La3CrAs5的高压合成、结构表征及物性研究

本文中,我们利用高温高压法,在La-Cr-As体系中发现并成功制备了第一个新的三元化合物材料La3CrAs5.该化合物属于六方反Hf5Sn3Cu型结构,其空间群为P3/mcm,晶格参数为a=b=8.9845A,c=5.8897A.La3CrAs5的晶体结构含有沿c轴方向的共面连接CrAs6八面体链,这些一维自旋链在ab平面内以三角格子形式进行排列,链与链之间的距离为8.9845A.研究表明,La3CrAs5具有三维金属导电性质,并且在低温条件下遵循费米液行为;另外,La3CrAs5中CrAs6自旋链由于巡游电子关联,在50K发生三维铁磁相变.理论计算表明,La对费米面附近态密度的贡献是不可忽略的,导致La3CrAs5成为了一个三维金属.此外,我们还计算了晶体轨道哈密顿数(-COHP)来解释La3CrAs5结构的整体稳定性以及化学键特征.

Orbital selection of the double [CuO2] layer compound Ca3Cu2O4Cl2

The discovery of high-temperature copper oxide superconductors(HTS)by Bednorz and Muller[1]in 1986 opened up a new field of superconductivity.Since then,several different families of materials have been discovered with greatly increased superconducting critical temperature(Tc)[2].Oxychloride cuprates,Can+1CunO2wCl2,are one such type of parent compound of high Tc cuprate superconductors.There are two members in this family known so far that can exist at ambient pressure:Ca2CuO2Cl2(single[Cu02]layer CCOC)and Ca3Cu2O4Cl2(double[CuO2]layer CCOC).Both are composed of a[CuO2]plane with the apical oxygen replaced by chlorine atoms.