Superconductivity in single crystals of ${\mathrm{ZrP}}_{1.27}{\mathrm{Se}}_{0.73}$

Superconductivity in single crystals of ${ZrP}_{1.27} {Se}_{0.73}$

K.-W. Chen, G. Chappell, S. Zhang, W. Lan, T. Besara, K. Huang, D. Graf, L. Balicas, A. P. Reyes, and R. E. Baumbach

Phys. Rev. B 102, 144522 – Published 22 October 2020

Abstract

Results are reported for single crystals of the PbFCl-type layered compound ${ZrP}_{1.27} {Se}_{0.73}$ that were produced using the iodine vapor transport method. Electrical transport, magnetization, and heat capacity measurements reveal disordered metallic behavior and the occurrence of bulk superconductivity, with a transition temperature $(T_{c})$ of 7.1 K and an anisotropic orbitally limited upper critical field. ${}^{31}P$ nuclear magnetic resonance measurements provide additional microscopic information, where the line shape, Knight shift, and spin-lattice relaxation data are consistent with the superconductivity originating from the corrugated Zr-P(2c)/Se plane. This suggests that the superconductivity first forms in the corrugated plane and the bulk superconductivity eventually occurs via coupling between the square planar layers. These data also show that either there are multiple superconducting gaps or there is a single gap that does not fully open across the entire Fermi surface. These results clarify the superconducting state in this material and will enable further measurements that require single-crystal specimens.

Received 27 May 2020
Revised 29 September 2020
Accepted 2 October 2020

DOI:https://doi.org/10.1103/PhysRevB.102.144522

Physics Subject Headings (PhySH)

Meissner effect Multiband superconductivity Superconducting gap Superconducting phase transition Symmetry protected topological states Topological superconductors

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

K.-W. Chen^1,2,3, G. Chappell^1,2, S. Zhang ^1,2, W. Lan ^1,2, T. Besara ⁴, K. Huang¹, D. Graf¹, L. Balicas¹, A. P. Reyes ¹, and R. E. Baumbach¹

¹National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA
²Department of Physics, Florida State University, Tallahassee, Florida 32306, USA
³Department of Physics, University of Michigan, Ann Arbor, Michigan 48109, USA
⁴Physics, Astronomy, and Materials Science Department, Missouri State University, Springfield, Missouri 65897, USA

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Vol. 102, Iss. 14 — 1 October 2020

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Figure 1
(a) Electrical resistivity $ρ$ vs temperature $T$ . The superconducting transition temperature $T_{c} = 7.1 K$ is defined as the temperature where $ρ (T)$ reaches zero. The right inset shows a typical single-crystal specimen. (b) The zero-field-cooled (ZFC) and field-cooled (FC) magnetic volume susceptibility under magnetic field $H = 10 Oe$ . The ZFC susceptibility saturates to a maximum value of $- 1 (1 / 4 π$ ) for $H ∥ c$ and $- 0.9 (1 / 4 π)$ for $H ∥ a b$ . (c) Specific heat $C$ divided by $T$ vs $T$ for $1.8 K \leq T \leq 10 K$ . The right inset shows $C / T$ vs $T^{2}$ where the dotted line is a fit to the data as described in the text. The left inset shows the electronic component of the heat capacity $C_{e} / T$ . The dotted lines represent an equal entropy construction used to define $T_{c}$ and the size of the jump.
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Figure 2
Temperature dependence of the electrical resistivity $ρ (T)$ in various magnetic fields $H$ close to the superconducting transition. Panels (a) and (b) show $H$ applied parallel $∥$ and perpendicular $⊥$ to the $c$ axis, respectively. Panels (c) and (d) show the upper critical fields $H_{c 2}$ vs $T$ for $H ∥$ and $⊥$ to the $c$ axis, respectively. The dashed lines are fits to the data using the Ginzburg-Landau theory.
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Figure 3
(a) The zero-field-cooled (ZFC) and field-cooled (FC) magnetic volume susceptibility under magnetic field $H = 10 Oe$ . The superconducting critical temperature $T_{c}$ is about 7.18 K. The maximum ZFC susceptibility is $- 0.9 (1 / 4 π$ ) for $H ∥ a b$ and $- 1 (1 / 4 π$ ) for $H ∥ c$ . (b) Magnetization $M$ vs magnetic field $H$ at various temperatures for ${ZrP}_{1.27} {Se}_{0.73}$ . The black solid line is fit to the 2 K data in the low-field linear region. (c) Fitting $H_{c 1}$ data by the formula $H_{c 1} (T) = H_{c 1} (0) [1 - {(T / T_{c})}^{2}]$ . The red solid line is the fitting curve.
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Figure 4
(a) Crystal structure of ${ZrP}_{2 - x} {Se}_{x}$ . Typical ${}^{31}P$ NMR spectra for $x = 0.73$ . The narrow line A is identified as originating from the square planar P(2a) sites and the broad line B from the corrugated planar P(2c) sites. (b) Angular dependence of ${}^{31}P$ spectra near $T_{c}$ and close to $H_{c 2}$ . The left peak A is saturated in these spectra because of its long recovery time.
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Figure 5
(a) Temperature dependence of ${}^{31}P$ spin-lattice relaxation in the P(2a) site (peak A) and (b) P(2c) site (peak B). For (b), the data are fitted with various modified BCS functions.
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Figure 6
(a) ${}^{31}P$ spin-lattice relaxation rate divided by temperature in the P(2a) site (peak A) and (b) for the P(2c) site (peak B) for $H ⊥ c$ . The loss in density of states below $T_{c}$ is clearly seen in peak B but not in A. The dashed line in (a) is a guide to the eye. Lines in (b) are the same fit as in Fig. 5.
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Physical Review B

covering condensed matter and materials physics

Superconductivity in single crystals of ${ZrP}_{1.27} {Se}_{0.73}$

K.-W. Chen, G. Chappell, S. Zhang, W. Lan, T. Besara, K. Huang, D. Graf, L. Balicas, A. P. Reyes, and R. E. Baumbach

Phys. Rev. B 102, 144522 – Published 22 October 2020

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Physical Review B

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Superconductivity in single crystals of ZrP1.27Se0.73

K.-W. Chen, G. Chappell, S. Zhang, W. Lan, T. Besara, K. Huang, D. Graf, L. Balicas, A. P. Reyes, and R. E. Baumbach

Phys. Rev. B 102, 144522 – Published 22 October 2020

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Superconductivity in single crystals of ${ZrP}_{1.27} {Se}_{0.73}$