arXiv subjects

Jürgen Haase

Publications and source records attributed to Jürgen Haase.

At least 19 recordsLinked to original sources

arXiv2025

Nanoscale lattice heterostructure in high Tc superconductors

Low temperature superconductivity was known since 1957 to be described by BCS theory for an effective single band metals controlled by the density of states at the Fermi level, very far from band edges, the electron phonon coupling, and the energy of the boson in the pairing interaction w0, but BCS has failed to predict high temperature superconductivity in different materials above about 23 K. High temperature superconductivity above 35 K since 1986 has been a matter of materials science where manipulating the lattice complexity of high temperature superconducting ceramic oxides (HTSC) has driven material scientists to grow new HTSC quantum materials up to 138K in HgBa2Ca2Cu3O8 (Hg1223) at ambient pressure and near room temperature in pressurized hydrides. This perspective covers the major results of materials scientist in these last 39 years investigating the role of lattice inhomogeneity detected in these new quantum complex materials. We highlight the nanoscale heterogeneity in these complex materials and elucidate their special role played in the physics for HTSC. Especially, it is pointed out that the geometry of lattice and charge complex heterogeneity at nanoscale is essential and intrinsic in the mechanism of rising quantum coherence at high temperature

cond-mat.supr-con↗

arXiv2023

17O enrichment of CaWO4 crystals for spin-dependent DM search

For many years, various experiments have attempted to shed light on the nature of dark matter (DM). This work investigates the possibility of using CaWO4 crystals for the direct search of spin-dependent DM interactions using the isotope 17O with a nuclear spin of 5/2. Due to the low natural abundance of 0.038%, an enrichment of the CaWO4 crystals with 17O is developed during the crystal production process at the Technical University of Munich. Three CaWO4 crystals were enriched, and their 17O content was measured by nuclear magnetic resonance spectroscopy at the University of Leipzig. This paper presents the concept and first results of the 17O enrichment and discusses the possibility of using enriched crystals to increase the sensitivity for the spin-dependent DM search with CRESST.

astro-ph.IM↗

arXiv2022

How pressure enhances the critical temperature of superconductivity in YBa$_2$Cu$_3$O$_{6+y}$

High-temperature superconducting cuprates respond to doping with a dome-like dependence of their critical temperature ($T_{\mathrm{c}}$). But the family specific maximum $T_\mathrm{c}$ can be surpassed by application of pressure, a compelling observation known for decades. We investigate the phenomenon with high-pressure anvil cell nuclear magnetic resonance (NMR) and measure the charge content at planar Cu and O, and with it the doping of the ubiquitous CuO$_2$ plane with atomic scale resolution. We find that pressure increases the overall doping, as widely assumed, but when it enhances $T_\mathrm{c}$ above what can be achieved by doping, it leads to a hole redistribution favoring planar O. This is similar to the observation that the family-specific maximum $T_\mathrm{c}$ also increases if the hole content at planar O is raised at the expense of that at planar Cu. Thus, the pressure-induced enhancement of $T_\mathrm{c}$ points to the same mechanism.

cond-mat.supr-con↗

arXiv2022

NMR study of AgInTe$_2$ at normal and high pressure

The ternary semiconductor AgInTe$_2$ is a thermoelectric material with chalcopyrite-type structure that transforms reversibly into a rocksalt-type structure under high pressure. Nuclear magnetic resonance (NMR) is considered to provide unique insight into material properties on interatomic length scales, especially in the context of structural phase transitions. Here, $^{115}$In and $^{125}$Te NMR is used to study AgInTe$_2$ for ambient conditions and pressures up to 5 GPa. Magnetic field dependent and magic angle spinning (MAS) experiments of $^{125}$Te prove strongly enhanced internuclear couplings, as well as a distribution of isotropic chemical shifts suggesting a certain degree of cation disorder. The indirect nuclear coupling is smaller for $^{115}$In, as well as the chemical shift distribution in agreement with the crystal structure. The $^{115}$In NMR is further governed by a small quadrupolar interaction ($ν_\mathrm{Q} \approx$ 90 kHz) and shows an orders of magnitude faster nuclear relaxation in comparison to that of $^{125}$Te. At a pressure of about 3 GPa, the $^{115}$In quadrupole interaction increases sharply to about 2400 kHz, indicating a phase transition to a structure with a well defined, though non-cubic local symmetry, while the $^{115}$In shift suggests no significant changes of the electronic structure. The NMR signal is lost above about 5 GPa (at least up to about 10 GPa). However, upon releasing the pressure a signal is recovered that points to the reported metastable ambient pressure phase with a high degree of disorder.

cond-mat.mtrl-sci↗

arXiv2022

A different NMR view of cuprate superconductors

Nuclear magnetic resonance (NMR) is a powerful quantum probe, but the early conclusions on the physics of the cuprates, based on a limited set of data, have to be revised in view of recent findings and results from extensive literature analyses of most NMR data. These show two coupled electronic spin components that influence the nuclei, most easily seen with the planar Cu shift anisotropy. One component is spin from the recently identified ubiquitous metallic excitations, the other due to the intrinsic, antiferromagnetically coupled electronic Cu spin. Both components and its intricate interaction leave their imprint on nuclear shifts and relaxation. They also show a family dependence seen in the charge sharing between planar Cu and O. The main phenomena of the doping and temperature dependences of the interplay between both spins components are discussed in terms of an apparent phenomenology that awaits explanation from theory.

cond-mat.supr-con↗

arXiv2022

Planar Cu and O NMR and the Pseudogap of Cuprate Superconductors

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 analyzed prior to the O data. The main finding is that the planar Cu shifts for one direction of the external magnetic field largely follow from the same states and pseudogap. This explains the shift suppression stated more recently, which leads to the failure of the Korringa relation in contrast to an enhancement of the relaxation due to antiferromagnetic spin fluctuations originally proposed. However, there is still the need for a second spin component that appears to be associated with the Cu $3d(x^2-y^2)$ hole to explain the complex Cu shift anisotropy and family dependence. Furthermore, it is argued that the planar Cu relaxation which was reported recently to be rather ubiquitous for the cuprates, must be related to this universal density of states and the second spin component, while not being affected by the simple pseudogap. Thus, while this universal metallic density of states with a pseudogap is also found in the planar Cu data, there is still need for a more elaborate scenario that eludes planar O.

cond-mat.supr-con↗

arXiv2021

Temperature independent pseudogap from $^{17}$O and $^{89}$Y NMR and the single component picture

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 proposed from the electronic entropy. Here we analyze the anisotropy of the shift and relaxation of planar O to establish whether a single electronic spin component is applicable, since the planar Cu shift anisotropy clearly fails such a description. We find that the orbital shift terms deduced from the data are in agreement with first principle calculations, and the shift data show a temperature independent anisotropy also in agreement with hyperfine coefficients predicted by first principles, which also account for the relaxation anisotropy. Furthermore, we show that the original $^{89}$Y shift and relaxation data are in agreement with the proposed temperature independent pseudogap. This pseudogap depends on doping, but also on the family of materials, and the density of states outside or in the absence of the gap is universal for the cuprates; this suggests that the entropy should be similar for all cuprates, as well. Further consequences will be discussed.

cond-mat.supr-con↗

arXiv2020

Temperature independent cuprate pseudogap from planar oxygen NMR

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 1500 K for the most underdoped systems, relating it to the exchange coupling. The pseudogap can vary substantially throughout a material, being the cause of cuprate inhomogeneity in terms of charge and spin, and consequences for the NMR analyses are discussed. This pseudogap appears to be in agreement with the specific heat data measured for the YBaCuO family of materials, long ago. Nuclear relaxation and shift show deviations from this scenario near $T_{\mathrm{c}}$, possibly due to other in-gap states.

cond-mat.supr-con↗

arXiv2020

NMR shift and relaxation and the electronic spin of superconducting cuprates

Very recently, there has been significant progress with establishing a common phenomenology of the superconducting cuprates in terms of nuclear magnetic resonance (NMR) shift and relaxation. Different from the old interpretation, it was shown that the shifts demand two coupled spin components with different temperature dependencies. One spin component couples isotropically to the planar Cu nucleus and is likely to reside at planar O, while the other, anisotropic component has its origin in the planar copper $3d(x^2-y^2)$ orbital. Nuclear relaxation, on the other hand, was found to be rather ubiquitous and Fermi liquid-like for planar Cu, i.e., it is independent of doping and material, apart from the sudden drop at the superconducting transition temperature, $T_{\rm c}$. However, there is a doping and material dependent anisotropy that is independent on temperature, above and below $T_{\rm c}$. Here we present a slightly different analysis of the shifts that fits all planar Cu shift data. In addition we are able to derive a simple model that explains nuclear relaxation based on these two spin components. In particular, the only outlier so far, \lsco, can be understood, as well. While this concerns predominantly planar Cu, it is argued that the two component model should fit all cuprate shift and relaxation data.

cond-mat.supr-con↗

arXiv2020

Unconventional $^{17}$O and $^{63}$Cu NMR shift components in cuprate superconductors

Nuclear magnetic resonance (NMR) is a fundamental bulk probe that provides key information about the electronic properties of materials. Very recently, the analysis of all available planar copper shift as well as relaxation data proved that while the shifts cannot be understood in terms of a single temperature dependent spin component, relaxation can be explained with one dominating Fermi liquid-like component, without enhanced electronic spin fluctuations. For the shifts, a doping dependent isotropic term, as well as doping independent anisotropic term became obvious. Here we focus on planar $^{17}$O NMR shifts and quadrupole splittings. Surprisingly, we find that they demand, independently, a similar two-component scenario and confirm most of the previous conclusions concerning the properties of the spin components, in particular that a negative spin polarization survives in the superconducting state. This should have consequences for the pairing scenario.

cond-mat.supr-con↗

arXiv2019

Phenomenology of $^{63}$Cu nuclear relaxation in cuprate superconductors

Nuclear relaxation is an important thermodynamic probe of electronic excitations, in particular in conducting and superconducting systems. Here, an empirical phenomenology based on all available literature data for planar Cu in hole-doped cuprates is developed. It is found that most of the seemingly different relaxation rates among the systems are due to a temperature independent anisotropy that affects the mostly measured $1/T_{1\parallel}$, the rate with an external magnetic field along the crystal $c$-axis, while $1/T_{1\perp}$ is largely independent on doping and material above the critical temperature of superconductivity ($T_c$). This includes very strongly overdoped systems that show Fermi liquid behavior and obey the Korringa law. Below $T_c$ the relaxation rates are similar, as well, if plotted against the reduced temperature $T/T_c$. Thus, planar Cu nuclear relaxation is governed by a simple, dominant mechanism that couples the nuclei with varying anisotropy to a rather ubiquitous bath of electronic excitations that appear Fermi liquid-like irrespective of doping and family. In particular, there is no significant enhancement of the relaxation due to electronic spin fluctuations, different from earlier conclusions. Only the La$_{2-x}$Sr$_x$CuO$_4$ family appears to be an outlier as additional relaxation is present, however, the anisotropy remains temperature independent. Also systems with very low doping levels, for which there is a lack of data, may behave differently.

cond-mat.supr-con↗

arXiv2019

Unusual $^{209}$Bi NMR quadrupole effects in topological insulator Bi$_2$Se$_3$

Three-dimensional topological insulators are an important class of modern materials, and a strong spin-orbit coupling is involved in making the bulk electronic states very different from those near the surface. Bi$_2$Se$_3$ is a model compound, and $^{209}$Bi NMR is employed here to investigate the bulk properties of the material with focus on the quadrupole splitting. It will be shown that this splitting measures the energy band inversion induced by spin-orbit coupling in quantitative agreement with first-principle calculations. Furthermore, this quadrupole interaction is very unusual as it can show essentially no angular dependence, e.g., even at the magic angle the first-order splitting remains. Therefore, it is proposed that the magnetic field direction is involved in setting the quantization axis for the electrons, and that their life time leads to a new electronically driven relaxation mechanism, in particular for quadrupolar nuclei like $^{209}$Bi. While a quantitative understanding of these effects cannot be given, the results implicate that NMR can become a powerful tool for the investigation of such systems.

cond-mat.mtrl-sci↗

arXiv2019

Properties of the electronic fluid of superconducting cuprates from $^{63}$Cu NMR shift and relaxation

Nuclear magnetic resonance (NMR) provides local, bulk information about the electronic properties of materials, and it has been influential for theory of high-temperature superconducting cuprates. Importantly, NMR found early that nuclear relaxation is much faster than what one expects from coupling to fermionic excitations above the critical temperature for superconductivity ($T_{\rm c}$), i.e. what one estimates from the Knight shift with the Korringa law. As a consequence, special electronic spin fluctuations have been invoked. Here, based on literature relaxation data it is shown that the electronic excitations, to which the nuclei couple with a material and doping dependent anisotropy, are rather ubiquitous and Fermi liquid-like. A suppressed NMR spin shift rather than an enhanced relaxation leads to the failure of the Korringa law for most materials. Shift and relaxation below $T_{\rm c}$ support the view of suppressed shifts, as well. A simple model of two coupled electronic spin components, one with $3d(x^2-y^2)$ orbital symmetry and the other with an isotropic $s$-like interaction can explain the data. The coupling between the two components is found to be negative, and it must be related to the pseudogap behavior of the cuprates. We can also explain the negative shift conundrum and the long-standing orbital shift discrepancy for NMR in the cuprates.

cond-mat.supr-con↗

arXiv2018

Proof of bulk charge ordering in the CuO$_2$ plane of the cuprate superconductor YBa$_2$Cu$_3$O$_{6.9}$ by high pressure NMR

Cuprate superconductors still hold many open questions, in particular concerning their normal state properties, including the role of charge ordering. Nuclear magnetic resonance on $^{63,65}$Cu and $^{17}$O in the CuO$_2$ plane is a very sensitive bulk probe of charge variations, but not properly understood. Since early NMR, the oxygen satellite line splittings in YBa$_2$Cu$_3$O$_{6+y}$ were attributed to the orthorhombic distortion, while they could also be due to charge ordering. We employ high pressure NMR on YBa$_2$Cu$_3$O$_{6.9}$ hoping that charge order would respond to pressure differently than the chemical lattice. That is what we find, and we prove the existence of charge ordering even at ambient conditions. As pressure increases we can follow its local symmetry and amplitude as function temperature. Our finding differ from what has been reported with other techniques so far, but also show similarities that will be discussed. We also offer evidence from literature NMR data that this charge ordering is ubiquitous to the CuO$_2$ plane.

cond-mat.supr-con↗

arXiv2018

Investigation of room temperature multispin-assisted bulk diamond 13C hyperpolarization at low magnetic fields

In this work we investigated the time behavior of the polarization of bulk 13C nuclei in diamond above the thermal equilibrium. This nonthermal nuclear hyperpolarization is achieved by cross relaxation between two nitrogen related paramagnetic defect species in diamond in combination with optical pumping. The decay of the hyperpolarization at four different magnetic fields is measured. Furthermore, we use the comparison with conventional nuclear resonance measurements to identify the involved distances of the nuclear spin with respect to the defects and therefore the coupling strengths. Also, a careful look at the linewidth of the signal give valuable information to piece together the puzzle of the hyperpolarization mechanism.

cond-mat.mes-hall↗

arXiv2017

Room temperature bulk diamond 13-C hyperpolarisation -- Strong evidence for a complex four spin coupling

Hyperpolarisation at room temperature is one of the most important research fields in order to improve liquid, gas or nanoparticle tracer for Magnetic Resonance Imaging (MRI) in medical applications. In this paper we utilize nuclear magnetic resonance (NMR) to investigate the hyperpolarisation effect of negatively charged nitrogen vacancy (NV) centres on carbon-13 nuclei and their spin diffusion in a diamond single crystal close to the excited state level anti crossing (ESLAC) around 50 mT. Whereas the electron spins of the NV centre can be easily polarized in its m = 0 ground state at room temperature just by irradiation with green light , the swop of the NV electron spin polarization to a carbon-13 nuclei is a complex task. We found that the coupling between the polarized NV electron spin, the electron spin of a substitutional nitrogen impurity (P1) as well as its nitrogen-14 nuclei and the carbon-13 nuclear spin has to be considered. Here we show that through an optimization of this procedure, in about two minutes a signal to noise ratio which corresponds to a 23 hour standard measurement without hyperpolarisation and an accumulation of 460 single scans can be obtained. Furthermore we were able to identify several polarisation peaks of different sign at different magnetic fields in a region of some tens of gauss. Most of the peaks can be attributed to a coupling of the NV centres to nearby P1 centres. We present a new theoretical model in a framework of cross polarisation of a four spin dynamic model in good agreement with our experimental data. The results demonstrate the opportunities and power as well as limitations of hyperpolarisation in diamond via NV centres. We expect that the current work may have a significant impact on future applications.

cond-mat.mes-hall↗

arXiv2017

Contrasting Phenomenology of NMR Shifts in Cuprate Superconductors

Nuclear magnetic resonance (NMR) shifts, if stripped off their uncertainties, must hold key information about the electronic fluid in the cuprates. The early shift interpretation that favored a single-fluid scenario will be reviewed, as well as recent experiments that reported its failure. Thereafter, based on literature shift data for planar Cu a contrasting shift phenomenology for cuprate superconductors is developed, which is very different from the early view while being in agreement with all published data. For example, it will be shown that the hitherto used hyperfine scenario is inadequate as a large isotropic shift component is discovered. Furthermore, the changes of the temperature dependences of the shifts above and below the superconducting transitions temperature proceed according to a few rules that were not discussed before. It appears that there can be substantial spin shift at the lowest temperature if the magnetic field lies in the CuO$_2$ plane, which points to a localization of spin in the $3d(x^2-y^2)$ orbital. A simple model is presented based on the most fundamental findings. The analysis must have new consequences for theory of the cuprates.

cond-mat.supr-con↗

arXiv2016

$^{77}$Se nuclear magnetic resonance of topological insulator Bi$_2$Se$_3$

Topological insulators (TIs) constitute a new class of materials with an energy gap in the bulk and peculiar metallic states on the surface. To date, most experiments have focused on probing the surface electronic structure of these materials. Here, we report on new and potentially interesting features resulting from the bulk electronic structure. Our findings are based on a comprehensive nuclear magnetic resonance (NMR) study of $^{77}$Se on Bi$_2$Se$_3$ and Cu$_{0.15}$Bi$_2$Se$_3$ single crystals. First, we find two resonance lines and show that they originate from the two inequivalent Se lattice sites. Second, we observe unusual field-independent linewidths, and attribute them to an unexpectedly strong internuclear coupling mediated by bulk electrons. These results call for a revision of earlier NMR studies and add insight into the bulk electronic properties of TIs.

cond-mat.mes-hall↗