Infrared spectroscopy study of the in-plane response of ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6.6}$ in magnetic fields up to 30 Tesla

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Infrared spectroscopy study of the in-plane response of ${YBa}_{2} {Cu}_{3} O_{6.6}$ in magnetic fields up to 30 Tesla

F. Lyzwa, B. Xu, P. Marsik, E. Sheveleva, I. Crassee, M. Orlita, and C. Bernhard

Phys. Rev. Research 2, 023218 – Published 22 May 2020

Abstract

With terahertz and infrared spectroscopy we studied the in-plane response of an underdoped, twinned ${YBa}_{2} {Cu}_{3} O_{6.6}$ single crystal with $T_{c} = 58 (1) K$ in high magnetic fields up to $B = 30$ Tesla (T) applied along the $c$ axis. Our goal was to investigate the field-induced suppression of superconductivity and to observe the signatures of the three-dimensional (3D) incommensurate copper charge density wave (Cu-CDW), which was previously shown to develop at such high magnetic fields. Our study confirms that a $B$ field in excess of 20 T gives rise to a full suppression of the macroscopic response of the superconducting condensate. However, it reveals surprisingly weak signatures of the 3D Cu-CDW at high magnetic fields. At 30 T there is only a weak reduction of the spectral weight of the Drude-response (by about 3%), which is accompanied by an enhancement of the so-called mid-infrared (MIR) band as well as a narrow electronic mode around $240 c m^{- 1}$ (and, possibly, another one around $90 c m^{- 1}$ ), which is interpreted in terms of a pinned phase mode of the CDW. The pinned phase mode and the MIR band are strong features already without magnetic field, which suggests that prominent but short-ranged and slowly fluctuating (compared to the picosecond infrared timescale) CDW correlations exist all along, i.e., even at zero magnetic field.

Received 19 December 2019
Accepted 1 April 2020

DOI:https://doi.org/10.1103/PhysRevResearch.2.023218

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Charge density waves Superconducting fluctuations Superconducting phase transition Superconductivity

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

F. Lyzwa^1,*, B. Xu¹, P. Marsik ¹, E. Sheveleva¹, I. Crassee ², M. Orlita², and C. Bernhard ^1,†

¹University of Fribourg, Department of Physics and Fribourg Center for Nanomaterials, Chemin du Musée 3, CH-1700 Fribourg, Switzerland
²Laboratoire National des Champs Magnétiques Intenses (LNCMI), CNRS-UGA-UPS-INSA, 25, Avenue des Martyrs, 38042 Grenoble, France

^*fryderyk.lyzwa@unifr.ch
^†christian.bernhard@unifr.ch

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Vol. 2, Iss. 2 — May - July 2020

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Figure 1
The $a b$ -plane response of a twinned, underdoped ${YBa}_{2} {Cu}_{3} O_{6.6}$ crystal in zero magnetic field and at selected temperatures above and below $T_{c} = 58 K$ shown in terms of (a) the reflectivity, (b) the real part of the optical conductivity $σ_{1}$ , and (c) the real part of the dielectric function $ɛ_{1}$ . Inset of (b): Superfluid density $Ω_{pS}^{2}$ at 12 K as deduced from the missing spectral weight in $σ_{1}$ according to the FGT sum rule (light blue line) and, alternatively, from the purely inductive term in the real part of the dielectric function (orange line). Inset of (c): Superconducting component in the real part of the dielectric function $ɛ_{1, SC}$ (magenta line) that has been obtained by subtracting the contribution of the regular part (black line), as derived via a KK analysis of $σ_{1} (ω > 0)$ , from the measured spectrum at 12 K (blue line).
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Figure 2
Reflectivity ratio between high and zero magnetic field of underdoped ${YBa}_{2} {Cu}_{3} O_{6.6}$ . (a) Evolution of the reflectivity ratio for different applied magnetic fields at 4.2 K. (b) Comparison of the magnetic field effect in the superconducting state [orange line; at 4.2 K] and the normal state [blue line; at 77 K]. (c) Comparison of the effect of suppressing superconductivity with a magnetic field of 30 T at 4.2 K (green line) and heating the sample to $65 K > T_{c}$ at 0 T (red line). The inset points out the enhanced dips around $200 c m^{- 1}$ and $80 c m^{- 1}$ , caused by the magnetic field. (d) Spectrum of the measured reflectivity ratio at 30 T and 4.2 K (green line) together with different extrapolations to higher energy that were used for a KK analysis of the data to obtain the spectra of the complex optical conductivity, σ, and the dielectric function, ε, shown in Fig. 3.
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Figure 3
Comparison of the effects of suppressing superconductivity in underdoped ${YBa}_{2} {Cu}_{3} O_{6.6}$ with $T_{c} = 58 K$ with a magnetic field of 30 T at 4.2 K and by increasing the temperature to 65 K at 0 T. (a), (b) Real parts of the optical conductivity $σ_{1}$ and the dielectric function $ɛ_{1}$ , respectively, in the superconducting state at $0 T, 12 K$ (blue lines) and in the normal state at $0 T, 65 K$ (red lines) and at 30 T, 4.2 K (green lines). The inset in (a) shows a magnified view of the suppression of $σ_{1}$ in the SC state. (c), (d) Difference plots between the spectra of $σ_{1}$ and $ɛ_{1}$ , respectively, when SC is suppressed at 30 T, 4.2 K and at 0 T, 65 K. The light blue line in (c) shows the contribution due to the reduction of the SW of the Drude peak at 30 T. The dark red lines in (c) and (d) show a fit that accounts for the transfer of SW at 30 T from the Drude peak towards the narrow peaks at 90 and $240 c m^{- 1}$ and a broad MIR band. Inset of (c): Magnified view of the effect of the different extrapolation procedures outlined in Fig. 2 on the $Δ σ_{1}$ spectrum. (e) Redistribution of the spectral weight (SW) lost by the Drude peak shown in terms of the frequency dependence of the integral of $Δ σ_{1}$ in panel (c), $SW (ω) = \int_{55 c m^{- 1}}^{ω^{'}} Δ σ_{1} (ω) d ω$ [in units of ( $10^{4} Ω^{- 1} c m^{- 2}$ )] for the different extrapolation procedures outlined in Fig. 2. (f) Schematic summary of the magnetic-field-induced spectral weight redistribution from the Drude peak to the narrow modes at 90 and $240 c m^{- 1}$ and the broad MIR band.
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Infrared spectroscopy study of the in-plane response of YBa2Cu3O6.6 in magnetic fields up to 30 Tesla

F. Lyzwa, B. Xu, P. Marsik, E. Sheveleva, I. Crassee, M. Orlita, and C. Bernhard

Phys. Rev. Research 2, 023218 – Published 22 May 2020

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Infrared spectroscopy study of the in-plane response of ${YBa}_{2} {Cu}_{3} O_{6.6}$ in magnetic fields up to 30 Tesla