arXiv subjects

Juergen Haase

Publications and source records attributed to Juergen Haase.

5 recordsLinked to original sources

arXiv2026

Hidden Universal Metal in Cuprate Superconductors

Nuclear relaxation is a very robust probe of electronic excitations in superconducting materials, above and below the critical temperature of superconductivity, $T_\mathrm{c}$. Here, a phenomenology of it in cuprate superconductors is established based on essentially all cuprate data available in the literature from the CuO$_2$ plane. A universal 'hidden metal' with $1/T_1 T = const$ reigns below the pseudogap line, and, similar to usual superconducting metals, all cuprates condense at $T_\mathrm{c}$ out of this metal and relaxation ceases rapidly. There is no Hebel-Slichter peak. Above the hidden metal, a renormalized two-component metal is found. Therefore, the hidden metal is identified as the pseudogap matter, which has other important properties. It predominantly lacks a uniform response, unlike the normal metal above $T^*$, and it does not significantly relax planar O. However, for planar Cu it exhibits a special relaxation anisotropy. With the field in the plane, it causes a relaxation rate that is very similar for all cuprates, $1/{^{63}T}_{1\perp}T\approx 25/$Ks, while with the field parallel to the $c$-axis, $1/{^{63}T}_{1\parallel}T$, the proportional rate (in the pseudogap range) changes as a function of doping and material. This relaxation anisotropy is strictly correlated with the maximum critical temperature, $T_\mathrm{c,max}$, of all cuprates. It is stipulated that two partially independent spin components are needed to understand this behavior. The new phenomenology will be discussed and should give a better foundation for the understanding of the cuprates

cond-mat.supr-con↗

arXiv2026

Pseudogap and Condensation in Cuprate Superconductors from NMR Shifts

The electronic properties of the high-temperature superconducting cuprates are encoded in complex sets of NMR data, but without microscopic theory, reliable NMR phenomenologies are in demand. Early analyses of NMR could only focus on very few materials and discovered spin singlet pairing and the enigmatic pseudogap. However, a coherent phenomenology of shift and relaxation could not be established, as incoming data from other cuprates complicated the picture. Today, due to work of many groups worldwide, planar copper and oxygen NMR data are available for most cuprates. Here, based only on symmetry of the two Cu hyperfine couplings, an anisotropic $A_α$ and isotropic $B$, the Cu shifts are disentangled, and two different shift components emerge. Upon doping the cuprates, metallic B-spins are created above the pseudogap temperature which is shared with metallic A-spins. Further doping decreases the pseudogap temperature and increases the B-spin, but less so the A-spin. The apparent linear rate of increase in density of states of the B-spin with doping increases nearly threefold above about $x=0.20$, where the pseudogap has disappeared and A and B turn into superconducting metals, i.e. they disappear rapidly at $T_\mathrm{c}$. The pseudogap temperature is a measure of the coupling between A and B, which suppresses the shifts but not nuclear relaxation. Spin singlet pairing involves A and B according to three simple rules for condensation which will be discussed. The optimal $T_\mathrm{c}$ demands a special match between A and B and involves systems with a pseudogap. However, the highest $T_\mathrm{c}$ of all cuprates is not encoded in the shift, but rather in nuclear relaxation and charge sharing between planar Cu and O. Relations to other probes are discussed.

cond-mat.supr-con↗

arXiv2025

Two-carrier description of cuprate superconductors from NMR

Cuprates currently hold the record for the highest temperature superconductivity at ambient pressure, but the microscopic understanding of these materials remains elusive. Here we utilize nuclear magnetic resonance (NMR) data of planar oxygen and copper from essentially all hole-doped cuprates to provide a universal phenomenology relating the NMR spin shifts, which measure the electronic spin polarization at a given nucleus, with the superconducting dome and maximum critical temperature. We demonstrate that there are two separate contributions to the spin shift at planar copper, only one of which is seen at oxygen, and associate them with two different carrier types. Upon disentangling these two components, their relative size is shown to determine not only the doping dependence of the superconducting dome, but also the variation in maximum superconducting critical temperature, $T_\mathrm{c}$, between different families. One of these components is independent of family and resides in the hybridized planar orbitals. The second component, in contrast, has a more three-dimensional character and encodes the differences between the families. It is thus related to the charge transfer gap and planar hole sharing. Our findings offer a key, universal insight which should prove useful in the continuing development of a comprehensive theory of the cuprates, as well as an indication of how it may be possible to engineer materials with higher critical temperatures.

cond-mat.supr-con↗

arXiv2025

Stripe-like correlations in the cuprates from oxygen NMR

Nuclear magnetic resonance (NMR) of planar oxygen, with its family independent phenomenology, is ideally suited to probe the nature of the quantum matter of superconducting cuprates. Here, with new experiments on La$_{2-x}$Sr$_x$CuO$_4$, in particular also at high doping levels, we report on short-range stripe-like correlations between local charge and spin. Their amplitudes at room temperature are nearly independent of doping up to at least $x=0.30$, only their relative phase slips near $x=1/4$. Comparisons show the correlations to be generic to the cuprates. Despite the atomic scale length, the variations still resemble the average spin and charge relation, which is not expected from the otherwise simple, apparently metallic behavior, even far into the overdoped regime. Perhaps the phase slip is at the heart of a quantum critical point that demands pseudogap behavior towards lower doping levels in an otherwise strange metal.

cond-mat.str-el↗

arXiv2009

Evidence for two electronic components in high-temperature superconductivity from NMR

A new analysis of 63Cu and 17O NMR shift data on La1.85Sr0.15CuO4 is reported that supports earlier work arguing for a two-component description of this material, but conflicts with the widely held view that the cuprates are a one-component system. The data are analyzed in terms of two components A and B with susceptibilities Chi(A), Chi(B), and Chi(AB)=Chi(BA) . We find that above Tc, Chi(AB) and Chi(BB) are independent of temperature and obtain for the first time the temperature dependence of all three susceptibilities above Tc as well as the complete temperature dependence of Chi(AA)+Chi(AB) and of Chi(AB)+Chi(BB) below Tc. The form of the results agrees with that recently proposed by Barzykin and Pines.

cond-mat.supr-con↗