A new NMR anvil cell design is used for measuring the influence of high pressure on the electronic properties of the high-temperature superconductor YBa$_2$Cu$_4$O$_8$ above the superconducting transition temperature $T_{\rm c}$. It is found that pressure increases the spin shift at all temperatures in such a way that the pseudo-gap feature has almost disappeared at 63 kbar. This change of the temperature dependent spin susceptibility can be explained by a pressure induced proportional decrease (factor of two) of a temperature dependent component, and an increase (factor of 9) of a temperature independent component, contrary to the effects of increasing doping. The results demonstrate that one can use anvil cell NMR to investigate the tuning of the electronic properties of correlated electronic materials with pressure.
Planar oxygen nuclear magnetic resonance (NMR) relaxation and shift data from all cuprate superconductors available in the literature are analyzed. They reveal a temperature independent pseudogap at the Fermi surface, which increases with decreasing doping in family specific ways, i.e., for some materials the pseudogap is substantial at optimal doping while for others it is nearly closed at optimal doping. The states above the pseudogap, or in its absence are similar for all cuprates and doping levels, and Fermi liquid-like. If the pseudogap is assumed exponential it can be as large as about 1…
Nuclear Magnetic Resonance (NMR) is a powerful local quantum probe of the electronic structure of materials, but in the absence of reliable theory the interpretation of the NMR data can be challenging. This is true in particular for the cuprate high-temperature superconductors. Over the years, a large base of NMR data became available, which makes a review of the early interpretation possible. Recently, it was shown that all planar $^{17}$O NMR shift and relaxation data available in the literature point to a temperature independent but doping dependent pseudogap, very similar to what was propo…
Carrier-Concentration Dependence of the Pseudogap Ground State of Superconducting Bi2Sr2-xLaxCuO6+delta Revealed by 63,65Cu-Nuclear Magnetic Resonance in Very High Magnetic Fields
Luttinger-volume violating Fermi liquid in the pseudogap phase of the cuprate superconductors
通过对Bi $_2$ Sr $_{2-x}$ La $_x$ CuO $_{6+δ}$(La-Bi 2201)在强磁场中的NMR测量,确定了铜氧化物中的非超导赝能隙相为Luttinger体积违反费米液体(LvvFL)。这种状态是零温度量子液体,不会破坏平移对称性,然而,费米表面包围的体积小于Luttinger定理给出的大体积。LvvFL中的小费米面包围的粒子数等于掺杂水平$p$,而不是总电子数$n_e=1-p$。分别用相位弦论和掺杂理论描述了LvvFL。对于dopon理论,我们可以得到一个半定量的协议与NMR实验。
Evidence of a critical hole concentration in underdoped YBa$_2$Cu$_3$O$_y$ single crystals revealed by $^{63}$Cu NMR
我们报道了一个$^{63}$ Cu NMR研究在去孪晶YBa $_2$ Cu $_3$ O $_y$单晶,重点是高度欠掺杂制度(y=6.35-6.6)。测量的光谱和自旋-晶格弛豫速率的$^{63}$铜揭示了静态秩序的出现在一个定义良好的起始温度$T_0$没有一个已知的序参数。虽然$T_0$随着空穴掺杂浓度$p$的增加而被快速抑制,但自旋赝能隙仅在$T_0\rightarrow 0$的掺杂含量附近和之上被识别。我们的数据表明,存在一个关键的空穴掺杂$p_c\sim 0.1$,这可能会控制静态秩序在$p<p_c$和自旋赝能隙在$p>p_c$。
Understanding the nature of the mysterious pseudogap phenomenon is one of the most important issues associated with cuprate high-$T_c$ superconductors. Here, we report $^{17}$O nuclear magnetic resonance (NMR) studies on two planar oxygen sites in stoichiometric cuprate YBa$_2$Cu$_4$O$_8$ to investigate the symmetry breaking inside the pseudogap phase. We observe that the Knight shifts of the two oxygen sites are identical at high temperatures but different below $T_{\rm nem} \sim$ 185 K, which is close to the pseudogap temperature $T^{\ast}$. Our result provides a microscopic evidence for int…
Single crystals of pristine and 6% Pd-intercalated 2H-TaSe$_2$ have been studied by means of $^{77}$Se nuclear magnetic resonance (NMR). The temperature dependence of the $^{77}$Se spectrum, with an unexpected line narrowing upon Pd intercalation, unravels the presence of correlated local lattice distortions far above the transition temperature of the charge density wave (CDW) order, thereby supporting a strong-coupling CDW mechanism in 2H-TaSe$_2$. While, the Knight shift data suggest that the incommensurate CDW transition involves a partial Fermi surface gap opening. As for spin dynamics, th…
Recently, an analysis of all available planar oxygen shift and relaxation data for the cuprate high-temperature superconductors showed that the data can be understood with a simple spin susceptibility from a metallic density of states common to all cuprates. It carries a doping dependent but temperature independent pseudogap at the Fermi surface, which causes the deviations from normal metallic behavior, also in the specific heat. Here, a more coherent, unbiased assessment of all data, including planar Cu, is presented and consequences are discussed, since the planar Cu data were collected and…
A weird electronic state accompanied with an anomalous superconducting precursor and/or exotic orders, called the pseudogap state, arises prior to a superconducting condensate in underdoped cuprates that are situated near Mott transition. Another way to make the system approach the Mott transition is the variation of bandwidth or correlation strength, which gives a new dimension to exploring this exotic state. Here we report nuclear magnetic resonance (NMR) studies on layered organic superconductors with half-filled bands whose widths are pressure-tuned near the Mott transition. The system sit…
The NMR spectrum of FeSe shows a dramatic broadening on cooling towards the bulk nematic phase at $T_s=90$ K, due to the formation of a quasi-static, short-range-ordered nematic domain structure. However, a quantitative understanding of the NMR broadening and its relationship to the nematic susceptibility is still lacking. Here, we show that the temperature and pressure dependence of the broadening is in quantitative agreement with the mean-field Edwards-Anderson parameter of an Ising-nematic model in the presence of random-field disorder introduced by non-magnetic impurities. Furthermore, the…
Correlation between Superconductivity and Magnetic Fluctuations in Fe(Se1-xSx) Revealed by 77Se NMR
我们目前的$^{77}$ Se-NMR测量FeSe $_{1-x}$ S $_x$样品与硫含量$x=0,9,15$和$29\%$。除了$x=29\%$之外,在所有样品的NMR光谱中观察到孪晶畴。NMR自旋-晶格弛豫速率表明,磁波动最初增强之间的$x=0\%$和$x=9\%$,但强烈抑制较高的$x$值。所观察到的行为的磁波动平行的超导转变温度$T_c$在这些材料中,提供了强有力的证据的主要重要性的磁波动的超导性,尽管在这个系统中存在的量子临界。
We report $^{121/123}$Sb nuclear quadrupole resonance (NQR) and $^{51}$V nuclear magnetic resonance (NMR) measurements on kagome metal CsV$_3$Sb$_5$ with $T_{\rm c}=2.5$ K. Both $^{51}$V NMR spectra and $^{121/123}$Sb NQR spectra split after a charge density wave (CDW) transition, which demonstrates a commensurate CDW state. The coexistence of the high temperature phase and the CDW phase between $91$ K and $94$ K manifests that it is a first order phase transition. At low temperature, electric-field-gradient fluctuations diminish and magnetic fluctuations become dominant. Superconductivity eme…
Paired Cluster Model of High-Tc Superconductivity:Explanation for Pseudogap Critical Concentration, Vortex Core Pseudogap and Possible Stripe Phase in High-Tc Superconductors
The recent discovery of superconductivity in doped infinite-layer nickelates has stimulated intensive interest, especially for similarities and differences compared to that in cuprate superconductors. In contrast to cuprates, although earlier magnetization measurement reveals a Curie-Weiss-like behavior in undoped infinite-layer nickelates, there is no magnetic ordering observed by elastic neutron scattering down to liquid helium temperature. Until now, the nature of the magnetic ground state in undoped infinite-layer nickelates was still elusive. Here, we perform a nuclear magnetic resonance …
A spin-triplet superconducting state mediated by ferromagnetic (FM) spin fluctuations has been suggested to occur in the newly discovered heavy-fermion superconductor UTe$_2$. However, the recent neutron scattering measurements revealed the presence of antiferromagnetic (AFM) spin fluctuations in UTe$_2$. Here, we report the $^{125}$Te nuclear magnetic resonance (NMR) studies of a single-crystal UTe$_2$, suggesting the coexistence of FM and AFM spin fluctuations in UTe$_2$. Owing to the two different Te sites in the compound, we conclude that the FM spin fluctuations are dominant within ladder…
Competition between the Pseudogap and Superconducting States of Bi$_{2}$Sr$_{2}$Ca$_{0.92}$Y$_{0.08}$Cu$_{2}$O$_{8+δ}$ Single Crystals Revealed by Ultrafast Broadband Optical Reflectivity
用超快宽带瞬态反射率实验研究了Bi $_{2}$ Sr $_{2}$ Ca $_{0.92}$ Y $_{0.08}$ Cu $_{2}$ O $_{8+δ}$中赝能隙的非平衡动力学与超导相的相互作用.一旦建立了超导电性,赝能隙的弛豫速度就会比正常状态快2倍,而相应的瞬态反射率变化在$\sim$ 0.5 ps后改变符号。$\sim$。结果可以用一组耦合的赝能隙和超导序参量的微分方程来描述。耦合项的符号和强度表明两相之间的竞争非常弱,允许它们共存。
An understanding of the missing antinodal electronic excitations in the pseudogap state is essential for uncovering the physics of the underdoped cuprate high temperature superconductors. The majority of high temperature experiments performed thus far, however, have been unable to discern whether the antinodal states are rendered unobservable due to their damping, or whether they vanish due to their gapping. Here we distinguish between these two scenarios by using quantum oscillations to examine whether the small Fermi surface pocket, found to occupy only 2% of the Brillouin zone in the underd…
We report results of a muon spin relaxation study of slow magnetic fluctuations in the pseudogap phase of underdoped single-crystalline YBa$_{2}$Cu$_{3}$O$_{y}$, $y = 6.77$ and 6.83. The dependence of the dynamic muon spin relaxation rate on applied magnetic field yields the rms magnitude~$B\mathrm{_{loc}^{rms}}$ and correlation time~$τ_c$ of fluctuating local fields at muon sites. The observed relaxation rates do not decrease with decreasing temperature~$T$ below the pseudogap onset at $T^\ast$, as would be expected for a conventional magnetic transition; both $B\mathrm{_{loc}^{rms}}$ and $τ_…
To investigate the normal-state magnetic properties of UTe2 under pressure, we perform 125Te nuclear magnetic resonance (NMR) measurements up to 2 GPa. Below 1.2 GPa, the b-axis NMR Knight shift shows a broad maximum at the so-called T_chimax on cooling, which is consistent with the magnetization measurement under pressure. T_chimax decreases with increasing pressure and disappears at the critical pressure Pc = 1.7 GPa, above which superconductivity is destroyed. This tendency is also observed in the temperature dependence of the nuclear spin-lattice relaxation rate 1/T1. At low pressures, 1/T…
Antiferromagnetic spin correlations and pseudogap-like behavior in Ca(Fe1-xCox)2As2 studied by 75As nuclear magnetic resonance and anisotropic resistivity
本文报道了在350~ $^{\circ}$ C退火7天的单晶Ca(Fe $_{1-x}$ Co $_x$)$_2$ As $_2$($x$ = 0.023,0.028,0.033和0.059)的$^{75}$ As核磁共振(NMR)测量结果。根据在条纹型反铁磁(AFM)状态下观察$^{75}$ As NMR谱的特征形状,如在$x$ = 0的情况下,($T_{\rm N}$ = 170 K),在$x$ = 0.023中观察到了与伴随的结构相变相称的AFM相变的明确证据($T_{\rm N}$ = 106 K)和$x$ = 0.028($T_{\rm N}$ = 53 K)。通过Knight位移和核自旋晶格弛豫速率的温度依赖性,(1/ $T_1$),尽管在顺磁状态下实现了与其他铁磷属元素化物超导体的情况一样的条纹型AFM自旋波动,但是我们发现AFM自旋波动在低于交叉温度$T^*$的情况下逐渐减小,该交叉温度几乎与Co取代浓度无关,并且归因于这些系统的自旋激发谱中的类赝隙行为。$T^*$特征发现与温度相关的平面间电阻率$ρ_c(T)$中的特征相关,但不与平面内电阻率$ρ_a (T)$相关。通过在平行和垂直于$c$轴的磁场下测量的1/ $T_1$数据,跟踪了各向异性条带型AFM自旋涨落在顺磁和赝能隙相中的温度演化。基于我们的NMR数据,我们在Ca(Fe $_{1-x}$ Co $_x$)$…
The discovery of a magnetic-field-induced charge-density-wave (CDW) order in the pseudogap state via nuclear magnetic resonance (NMR) studies has highlighted the importance of "charge" in the physics of high transition-temperature ($T_{\rm c}$) superconductivity in copper oxides (cuprates). Herein, after briefly reviewing the progress achieved in the last few years, we report new results of $^{63,65}$Cu-NMR measurements on the CDW order and its fluctuation in the single-layered cuprate Bi$_2$Sr$_{2-x}$La$_x$CuO$_{6+δ}$. The NMR spectrum under both in- and out-of-plane magnetic fields above $ H…