arXiv subjects

Genda Gu

Publications and source records attributed to Genda Gu.

168 records · Page 10Linked to original sources

arXiv2009

Magnetic field control of charge structures in the magnetically disordered phase of the multiferroic LuFe$_2$O$_4$

Using neutron diffraction, we have studied the magnetic field effect on charge structures in the charge-ordered multiferroic material LuFe$_2$O$_4$. An external magnetic field is able to change the magnitude and correlation lengths of the charge valence order even before the magnetic order sets in. This affects the dielectric and ferroelectric properties of the material and induces a giant magneto-electric effect. Our results suggest that the magneto-electric coupling in LuFe$_2$O$_4$ is likely due to magnetic field effect on local spins, in clear contrast to the case in most other known multiferroic systems where the bulk magnetic order is important.

cond-mat.str-el↗

arXiv2008

Magnetic field induced enhancement of spin-order peak intensity in La(1.875)Ba(0.125)CuO(4)

We report on neutron-scattering results on the impact of a magnetic field on stripe order in the cuprate La$_{1.875}$Ba$_{0.125}$CuO$_4$. It is found that a 7 T magnetic field applied along the {\it c} axis causes a small but finite enhancement of the spin-order peak intensity and has no observable effect on the peak width. Inelastic neutron-scattering measurements indicate that the low-energy magnetic excitations are not affected by the field, within experimental error. In particular, the small energy gap that was recently reported is still present at low temperature in the applied field. In addition, we find that the spin-correlation length along the antiferromagnetic stripes is greater than that perpendicular to them.

cond-mat.supr-con↗

arXiv2008

Electronic Origin of the Inhomogeneous Pairing Interaction in the High-Tc Superconductor Bi2Sr2CaCu2O8+d

Identifying the mechanism of superconductivity in the high-temperature cuprate superconductors is one of the major outstanding problems in physics. We report local measurements of the onset of superconducting pairing in the high-transition temperature (Tc) superconductor Bi2Sr2CaCu2O8+d using a lattice-tracking spectroscopy technique with a scanning tunneling microscope. We can determine the temperature dependence of the pairing energy gaps, the electronic excitations in the absence of pairing, and the effect of the local coupling of electrons to bosonic excitations. Our measurements reveal that the strength of pairing is determined by the unusual electronic excitations of the normal state, suggesting that strong electron-electron interactions rather than low-energy (<0.1 volts) electron-boson interactions are responsible for superconductivity in the cuprates.

cond-mat.supr-con↗

arXiv2006

Incommensurate lattice distortion in the high temperature tetragonal phase of La$_{2-x}$(Sr,Ba)$_{x}$CuO$_{4}$

We report incommensurate diffuse (ICD) scattering appearing in the high-temperature-tetragonal (HTT) phase of La$_{2-x}$(Sr,Ba)$_{x}$CuO$_{4}$ with $0.07 \leq x \leq 0.20$ observed by the neutron diffraction technique. For all compositions, a sharp superlattice peak of the low-temperature-orthorhombic (LTO) structure is replaced by a pair of ICD peaks with the modulation vector parallel to the CuO$_6$ octahedral tilting direction, that is, the diagonal Cu-Cu direction of the CuO$_2$ plane, above the LTO-HTT transition temperature $T_s$. The temperature dependences of the incommensurability $δ$ for all samples scale approximately as $T/T_s$, while those of the integrated intensity of the ICD peaks scale as $(T-T_s)^{-1}$. These observations together with absence of ICD peaks in the non-superconducting $x=0.05$ sample evince a universal incommensurate lattice instability of hole-doped 214 cuprates in the superconducting regime.

cond-mat.supr-con↗

arXiv2004

Reply to "Sharp-mode coupling in High-Tc Superconductors"

Our optical technique has the advantage of being a bulk probe, which is less subject to uncertainties in the doping level and in the quality of the surface than angle resolved photoemission (ARPES). It is also capable of higher energy resolution and the overall noise level is lower. The disadvantage is that it gives momentum averaged properties. In light of these differences, it came as a surprise to us that our reported optical self-energies were able to track in accurate detail the ARPES self-energies of Johnson et al. Our data indicate that, as a function of doping, not only could both optical and ARPES techniques resolve the sharp mode from the background but also that the sharp mode intensity decreases uniformly, disappearing completely at a doping level of 0.23. As superconductivity is still strong at this doping level, with a Tc of 55 K, we conclude that the sharp mode was not an important contributor to high-temperature superconductivity.

cond-mat.supr-con↗

arXiv2004

Response to comment by Cuk et al

In a recent study of the optical conductivity of the Bi-2212 high temperature superconductor, Hwang, et al. have confirmed the mass-renormalization changes observed in ARPES but find that such changes are no longer observed in the highly overdoped regime. In a comment on this study, Cuk, et al. challenge this conclusion and present ARPES evidence for a kink in the superconducting state in the highly overdoped regime. We show, however that two doping dependent properties in the data of Cuk et al., the frequencies of the superconducting gap and the Van Hove singularity, suggest a Tc that is higher than the 58 K quoted, and that their sample is not as highly overdoped as claimed. As a result, these data can not refute the claim of Hwang et al. that the kink is absent in the highly overdoped region.

cond-mat.supr-con↗