Effects of strain on the electronic structure, superconductivity, and nematicity in FeSe studied by angle-resolved photoemission spectroscopy

G. N. Phan, K. Nakayama, K. Sugawara, T. Sato, T. Urata, Y. Tanabe, K. Tanigaki, F. Nabeshima, Y. Imai, A. Maeda, and T. Takahashi

Phys. Rev. B 95, 224507 – Published 9 June 2017

Abstract

One of central issues in iron-based superconductors is the role of structural change to the superconducting transition temperature ( $T_{c}$ ). It was found in FeSe that the lattice strain leads to a drastic increase in $T_{c}$ , accompanied by suppression of nematic order. By angle-resolved photoemission spectroscopy on tensile- or compressive-strained and strain-free FeSe, we experimentally show that the in-plane strain causes a marked change in the energy overlap ( $Δ E_{h - e}$ ) between the hole and electron pockets in the normal state. The change in $Δ E_{h - e}$ modifies the Fermi-surface volume, leading to a change in $T_{c}$ . Furthermore, the strength of nematicity is also found to be characterized by $Δ E_{h - e}$ . These results suggest that the key to understanding the phase diagram is the fermiology and interactions linked to the semimetallic band overlap.

Received 21 April 2016
Revised 28 April 2017

DOI:https://doi.org/10.1103/PhysRevB.95.224507

Physics Subject Headings (PhySH)

Superconductivity

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

G. N. Phan¹, K. Nakayama¹, K. Sugawara², T. Sato¹, T. Urata^1,*, Y. Tanabe¹, K. Tanigaki^1,2, F. Nabeshima³, Y. Imai^3,†, A. Maeda³, and T. Takahashi^1,2

¹Department of Physics, Tohoku University, Sendai 980-8578, Japan
²WPI Research Center, Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
³Department of Basic Science, the University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan

^*Present address: Department of Crystalline Materials Science, Nagoya University, Nagoya 464-8603, Japan.
^†Present address: Department of Physics, Tohoku University, Sendai 980-8578, Japan.

Article Text (Subscription Required)

Click to Expand

Supplemental Material (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 95, Iss. 22 — 1 June 2017

Reuse & Permissions

Access Options

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
Comparison of electronic structure among bulk FeSe, ${FeSe / CaF}_{2}$ , and ${FeSe / SrTiO}_{3}$ . (a) ARPES intensity map at $E_{F}$ as a function of the two-dimensional wave vector measured in the nematic phase ( $T$ = 30 K) for strain-free bulk FeSe ( $T_{c} \sim$ 8 K). The intensity was obtained by integrating the spectral intensity within $\pm 10$ meV with respect to $E_{F}$ . (b) Near- $E_{F}$ ARPES intensity plot for bulk FeSe as a function of binding energy and wave vector measured in the normal state ( $T$ = 120 K) along cuts 1 and 2 shown in (a). The data were divided by the Fermi-Dirac function convoluted with the instrumental resolution. Dashed curves are a guide for the eyes to trace the band dispersions. (c) Near- $E_{F}$ ARPES intensity measured at $T$ = 30 K along cuts 2 and 3 in (a). (d)–(f) and (g)–(i): Same as (a)–(c), but for compressive-strained ${FeSe / CaF}_{2}$ ( $T_{c} \sim$ 12 K) and tensile-strained ${FeSe / SrTiO}_{3}$ ( $T_{c} \sim$ 0 K), respectively. The ARPES intensities in (e) and (h) were measured at $T$ = 120 K and 190 K, respectively. (j) Second-derivative intensity plot measured along cut 4 in (g) at $T$ = 100 K, obtained after dividing by the Fermi-Dirac function convoluted with the instrumental resolution. Blue dashed lines are a guide for the eyes to trace the Dirac-cone-like dispersion. (k) Schematic illustration of Dirac-cone dispersion around the $M$ point. Blue, light blue, pink, and red arrows highlight the Lifshitz transition of FS. The former two highlight the case of ${FeSe / SrTiO}_{3}$ , while the latter two the case of bulk FeSe and ${FeSe / CaF}_{2}$ .
Reuse & Permissions
Figure 2
Strain-induced evolution of band dispersions. (a) Comparison of near- $E_{F}$ band dispersions around the $Γ$ point in the normal state ( $T$ = 120–190 K) for ${FeSe / SrTiO}_{3}$ , bulk FeSe, and ${FeSe / CaF}_{2}$ . (b) and (c): Same as (a), but measured around the $M$ point at high temperature ( $T$ = 120–190 K) and low temperature ( $T$ = 30 K), respectively. Filled circles were extracted from the peak maxima in ARPES spectra shown in Fig. 1. Open circles for the $δ$ band were extracted from the second-derivative plots in Supplemental Material [20] Fig. S2. Dashed curves are a guide for the eyes to trace the band dispersions. Green shade in (a)–(c) highlights the top of the $α^{'}$ band, the bottom of the $γ$ band, and the energy scale of $Δ E_{nem}$ , respectively.
Reuse & Permissions
Figure 3
Relationship between semimetallic band gap and some key physical parameters. (a)–(c) Schematics of normal-state band structure for tensile-strained, strain-free, and compressive-strained FeSe, respectively. Pink dots indicate the position of van Hove singularity at the $M$ point, while red arrows highlight the magnitude of $Δ E_{h - e}$ , which is the energy difference between the $α^{'}$ -band top and the $γ$ -band bottom. (d) Electronic phase diagram of FeSe as a function of in-plane lattice constant $a$ [5, 7, 14]. (e)–(g) Schematics of the band structure in the nematic state for tensile-strained phase, at a critical point of the Lifshitz transition, and for the compressive-strained phase, respectively. Yellow dots indicate the position of the Dirac point. (h) Strain dependence of $T_{c}$ and hole/electron carrier concentration at $T$ = 30 K plotted as a function of $Δ E_{h - e}$ . (i) Plot of $Δ E_{nem}$ (energy difference between the $ɛ_{1}$ and $ɛ_{2}$ bands at the $M$ point) as a function of $Δ E_{h - e}$ .
Reuse & Permissions

Physical Review B

covering condensed matter and materials physics