We give a quantitative analysis of the previously published nuclear magnetic resonance (NMR) experiments in the k-(ET)2X family of organic charge transfer salts by using the phenomenological spin fluctuation model of Moriya, and Millis, Monien and Pines (M-MMP). For temperatures above T_nmr ~ 50 K, the model gives a good quantitative description of the data in the metallic phases of several k-(ET)2X materials. These materials display antiferromagnetic correlation lengths which increase with decreasing temperature and grow to several lattice constants by T_nmr. It is shown that the fact that the dimensionless Korringa ratio is much larger than unity is inconsistent with a broad class of theoretical models (such as dynamical mean-field theory) which neglects spatial correlations and/or vertex corrections. For materials close to the Mott insulating phase the nuclear spin relaxation rate, the Knight shift and the Korringa ratio all decrease significantly with decreasing temperature below T_nmr. This cannot be described by the M-MMP model and the most natural explanation is that a pseudogap, similar to that observed in the underdoped cuprate superconductors, opens up in the density of states below T_nmr. Such a pseudogap has recently been predicted to occur in the dimerised organic charge transfer salts materials by the resonating valence bond (RVB) theory. We propose specific new experiments on organic superconductors to elucidate these issues. For example, measurements to see if high magnetic fields or high pressures can be used to close the pseudogap would be extremely valuable.
Shubnikov-de Haas effect and Yamaji oscillations in the antiferromagnetically ordered organic superconductor k-(BETS)2FeBr4: A Fermiology study
在有机超导体$κ$ -（BETS）$_2$ FeBr $_4$中观察到了Shubnikov-De Haas效应（SdH）和角相关磁电阻振荡（AMRO）。与其同构化合物$κ-(BETS)$ _2 $FeCl$ _4 $, SdH oscillations, for fields perpendicular to the conducting planes, reveal three Fermi Surface (FS) closed orbits $ α $, $ β $, and $ γ $ whose cross sectional areas are 19.8 %, 99.9 %, and 2.4 % of the first Brillouin zone, respectively. The conduction electron effective masses were found to be: $ μ_α =（4.7 \pm 0.2）$ m$ _e $, $ μ_β =（8.0 \pm 1.0）$ m$ _e $, and $ μ_γ =（2.0 \pm 0.2）$ m$ _e $. The observation of a $ γ $ orbit is not expected from band structure calculations, $ μ_β $ is …
The band structure and magnetic properties of organic charge-transfer salt $λ$-(BEDSe-TTF)$_2$GaCl$_4$ (BEDSe-TTF: bis(ethylenediseleno)tetrathiafulvalene; abbreviated as $λ$-BEDSe) are investigated. The reported crystal structure is confirmed using X-ray diffraction measurements, and the transfer integrals are calculated. The degree of electron correlation $U/W$ ($U$: on-site Coulomb repulsion, $W$: bandwidth) of $λ$-BEDSe is larger than one and comparable to that of the isostructural Mott insulator $λ$-(ET)$_2$GaCl$_4$ (ET: bis(ethylenedithio)tetrathiafulvalene, abbreviated as $λ$-ET), where…
Towards a consistent picture for quasi-1D organic superconductors
最近在低温下测量了准一维有机超导体（TMTSF）2 PF 6的电阻率，从抑制自旋密度波态所需的临界压力到超导性几乎消失的压力。该数据揭示了在Tc处超导性的开始与正常状态电阻率中的非费米液体线性项的强度之间的直接相关性，在低温下为r（T）= r 0 + AT + BT 2，因此当Tc变为0时，A变为0。在这里，我们表明，低频反铁磁波动的自旋晶格弛豫速率的贡献也与此非费米液体项AT的电阻率。这些相关性表明，异常散射和配对有一个共同的起源，都植根于低频反铁磁波动测量核磁共振。类似的情况也可能在最近发现的铁-磷属元素化物超导体中普遍存在。
Spin Liquid State in an Organic Mott Insulator with Triangular Lattice
在具有近各向同性三角晶格的有机莫特绝缘体体$κ$ -（BEDT-TTF）$_{2}$ Cu $_{2}$（CN）$_{3}$中进行了$^{1}$ H NMR和静态磁化率测量。静态磁化率用自旋$S$ = 1/2反铁磁三角格子海森堡模型描述，交换常数为$J$ 250 K.不管大的磁相互作用，$^{1}$ H NMR谱显示，在低至32 mK（比$J$小四个数量级）的范围内，没有长程磁有序的迹象。这些结果表明，量子自旋液体状态是实现在压力下出现的超导状态的紧密接近。
We report magnetoresistance and Hall Effect results for electron-doped films of the high-temperature superconductor La$_{2-x}$Ce$_x$CuO$_4$ (LCCO) for temperatures from 0.7 to 45 K and magnetic fields up to 65 T. For x = 0.12 and 0.13, just below the Fermi surface reconstruction (FSR), the normal state in-plane resistivity exhibits a well-known upturn at low temperature. Our new results show that this resistivity upturn is eliminated at high magnetic field and the resistivity becomes linear-in-temperature from $\sim$ 40 K down to 0.7 K. The magnitude of the linear coefficient scales with Tc an…
Magnetic-field-angle-resolved heat capacity of dimer-Mott organic superconductors $κ$-(BEDT-TTF)$_2$$X$ is reported. Temperature and field dependence of heat capacity indicates that the superconductivity has line nodes on the Fermi surface, which is a typical feature of $d$-wave superconductivity. In-plane field-angle dependence exhibits fourfold oscillations as well as twofold oscillations due to anisotropy of superconducting gap functions. From analyses of the fourfold term, the gap symmetry is determined as $d_{x^{2}-y^{2}}$+$s_{\pm}$ for $X$=Cu[N(CN)$_2$]Br and $d_{xy}$ for $X$=Ag(CN)$_2$H…
Different superconducting percolation regimes in the layered organic Mott system $κ$-(BEDT-TTF)$_2$Cu[N(CN)$_2$]Cl -- evidence from fluctuation spectroscopy
We show that a static electric field induces the transition from a ferromagnetic metal to an antiferromagnetic insulator owing to the Bloch oscillation of conduction electrons. In the steady state, the electric current is inversely proportional to the applied electric field, implying the nonperturbative insulating nature that is different from the Wannier-Stark localization. Possible experimental realization based on recent terahertz pulse sources is discussed.
Magnetic correlations and quantum criticality in the insulating antiferromagnetic, insulating spin liquid, renormalized Fermi liquid, and metallic antiferromagnetic phases of the Mott system V_2O_3
Sr2IrO4 is an archetypal spin-orbit-coupled Mott insulator with an antiferromagnetic state below 240 K. Here we report results of our study on single crystals of Sr2Ir1-xFexO4 (0<x<0.32) and Sr2Ir1-xCoxO4 (0<x<0.22). Fe doping retains the antiferromagnetic state but simultaneously precipitates an emergent metallic state whereas Co doping causes a rapid collapse of both the antiferromagnetic and Mott states, giving rise to a confined metallic state featuring a pronounced linearity of the basal-plane resistivity up to 700 K. The results indicate tetravalent Fe4+(3d4) ions in the intermediate spi…
We identify a mechanism to convert skyrmions and antiskyrmions into their antiferromagnetic (AFM) counterparts via interfacial engineering. The key idea is to combine properties of an antiferromagnet and a spin-orbit (SO) coupled metal. Utilizing hybrid Monte Carlo (HMC) simulations for a generic microscopic electronic Hamiltonian for the interfacial layers, we explicitly show the emergence of AFM skyrmions and AFM antiskyrmions. We further show that an effective spin Hamiltonian provides a simpler understanding of the results. We discuss the role of electronic itinerancy in determining the na…
