Magnetotransport evidence of irreversible spin reorientation in the collinear antiferromagnetic state of underdoped Nd2−xCexCuO4\mathrm{Nd}_{2-x}\mathrm{Ce}_x\mathrm{CuO}_4

We make use of the strong spin-charge coupling in the electron-doped cuprate $\mathrm{Nd}_{2-x}\mathrm{Ce}_x\mathrm{CuO}_4$ to probe changes in its spin system via magnetotransport measurements. We present a detailed study of the out-of-plane magnetoresistance in underdoped single crystals of this compound, including the nonsuperconducting, $0.05\,\leq x\,\leq 0.115$, and superconducting, $0.12\,\leq x\,\leq 0.13$, compositions. Special focus is put on the dependence of the magnetoresistance on the field orientation in the plane of the CuO$_2$ layers. In addition to the kink at the field-induced transition between the noncollinear and collinear antiferromagnetic configurations, a sharp irreversible feature is found in the angle-dependent magnetoresistance of all samples in the high-field regime, at field orientations around the Cu--O--Cu direction. The obtained behavior can be explained in terms of field-induced reorientation of Cu$^{2+}$ spins within the collinear antiferromagnetic state. It is, therefore, considered as an unambiguous indication of the long-range magnetic order

Magnetic excitations and amplitude fluctuations in insulating cuprates

We present results from light scattering experiments on three insulating antiferromagnetic cuprates, YBa$_2$Cu$_3$O$_{6.05}$, Bi$_2$Sr$_2$YCu$_2$O$_{8+\delta}$, and La$_2$CuO$_4$ as a function of polarization and excitation energy {using samples of the latest generation. From the raw data we derive symmetry-resolved spectra.} The spectral shape in $B_{1g}$ symmetry is found to be nearly universal and independent of the excitation energy. The spectra agree quantitatively with predictions by field theory [\onlinecite{Weidinger:2015}] facilitating the precise extraction of the Heisenberg coupling $J$. {In addition, the asymmetric line shape on the high-energy side is found to be related to amplitude fluctuations of the magnetization. In La$_2$CuO$_4$ alone minor contributions from resonance effects may be identified.} The spectra in the other symmetries are not universal. The variations may be traced back to weak resonance effects and extrinsic contributions. For all three compounds we find support for the existence of chiral excitations appearing as a continuum in $A_{2g}$ symmetry having an onset slightly below $3J$. In La$_2$CuO$_4$ an additional isolated excitation appears on top of the $A_{2g}$ continuum.Comment: 8 pages, 7 figure

Revisiting the vortex-core tunnelling spectroscopy in YBa2_2Cu3_3O7−δ_{7-\delta}

The observation by scanning tunnelling spectroscopy (STS) of Abrikosov vortex cores in the high-temperature superconductor YBa$_2$Cu$_3$O$_{7-\delta}$ (Y123) has revealed a robust pair of electron-hole symmetric states at finite subgap energy. Their interpretation remains an open question because theory predicts a different signature in the vortex cores, characterised by a strong zero-bias conductance peak. We present STS data on very homogeneous Y123 at 0.4 K revealing that the subgap features do not belong to vortices: they are actually observed everywhere along the surface with high spatial and energy reproducibility, even in the absence of magnetic field. Detailed analysis and modelling show that these states remain unpaired in the superconducting phase and belong to an incoherent channel which contributes to the tunnelling signal in parallel with the superconducting density of states.Comment: Final version with supplementary materia

Evaluation of T1 relaxation time in prostate cancer and benign prostate tissue using a Modified Look-Locker inversion recovery sequence

Purpose of this study was to evaluate the diagnostic performance of T1 relaxation time (T1) for differentiating prostate cancer (PCa) from benign tissue as well as high- from low-grade PCa. Twenty-three patients with suspicion for PCa were included in this prospective study. 3 T MRI including a Modified Look-Locker inversion recovery sequence was acquired. Subsequent targeted and systematic prostate biopsy served as a reference standard. T1 and apparent diffusion coefficient (ADC) value in PCa and reference regions without malignancy as well as high- and low-grade PCa were compared using the Mann-Whitney U test. The performance of T1, ADC value, and a combination of both to differentiate PCa and reference regions was assessed by receiver operating characteristic (ROC) analysis. T1 and ADC value were lower in PCa compared to reference regions in the peripheral and transition zone (p < 0.001). ROC analysis revealed high AUCs for T1 (0.92; 95%-CI, 0.87-0.98) and ADC value (0.97; 95%-CI, 0.94 to 1.0) when differentiating PCa and reference regions. A combination of T1 and ADC value yielded an even higher AUC. The difference was statistically significant comparing it to the AUC for ADC value alone (p = 0.02). No significant differences were found between high- and low-grade PCa for T1 (p = 0.31) and ADC value (p = 0.8). T1 relaxation time differs significantly between PCa and benign prostate tissue with lower T1 in PCa. It could represent an imaging biomarker for PCa

Exchange-enhanced Ultrastrong Magnon-Magnon Coupling in a Compensated Ferrimagnet

The ultrastrong coupling of (quasi-)particles has gained considerable attention due to its application potential and richness of the underlying physics. Coupling phenomena arising due to electromagnetic interactions are well explored. In magnetically ordered systems, the quantum-mechanical exchange-interaction should furthermore enable a fundamentally different coupling mechanism. Here, we report the observation of ultrastrong intralayer exchange-enhanced magnon-magnon coupling in a compensated ferrimagnet. We experimentally study the spin dynamics in a gadolinium iron garnet single crystal using broadband ferromagnetic resonance. Close to the ferrimagnetic compensation temperature, we observe ultrastrong coupling of clockwise and anticlockwise magnon modes. The magnon-magnon coupling strength reaches more than 30% of the mode frequency and can be tuned by varying the direction of the external magnetic field. We theoretically explain the observed phenomenon in terms of an exchange-enhanced mode-coupling mediated by a weak cubic anisotropy

How pressure enhances the critical temperature of superconductivity in YBa2_{2}Cu3_{3}O6+y_{6+y}

High-temperature superconducting cuprates respond to doping with a dome-like dependence of their critical temperature (Tc). But the family-specific maximum Tc can be surpassed by application of pressure, a compelling observation known for decades. We investigate the phenomenon with high-pressure anvil cell NMR and measure the charge content at planar Cu and O, and with it the doping of the ubiquitous CuO2 plane with atomic-scale resolution. We find that pressure increases the overall hole doping, as widely assumed, but when it enhances Tc above what can be achieved by doping, pressure leads to a hole redistribution favoring planar O. This is similar to the observation that the family-specific maximum Tc is higher for materials where the hole content at planar O is higher at the expense of that at planar Cu. The latter reflects dependence of the maximum Tc on the Cu–O bond covalence and the charge-transfer gap. The results presented here indicate that the pressure-induced enhancement of the maximum Tc points to the same mechanism