Pis’ma v ZhETF, vol. 116, iss. 11, pp. 777 - 778
© 2022 December 10
Orbital selective localization enhancement in Ca2-xSrxRuO4
A. O. Shorikov+∗1), D. Y. Novoselov+∗, D. M. Korotin+, V. I. Anisimov+∗
+M. N. Mikheev Institute of Metal Physics of Ural Branch of the Russian Academy of Sciences, 620108 Yekaterinburg, Russia
∗Department of Theoretical Physics and Applied Mathematics, Ural Federal University, 620002 Yekaterinburg, Russia
Submitted 29 September 2022
Resubmitted 20 October 2022
Accepted 20
October 2022
DOI: 10.31857/S1234567822230069, EDN: mdqpee
The discovery of unconventional superconductivity
of the continuous-time quantum Monte Carlo method
at Tc = 0.93 K in Sr2RuO4 which is isostructural to
(CT-QMC) [12] as implemented in the AMULET
High-Tc layered copper-based perovskites [1, 2] moti-
package [13]. QMC calculations were performed for
vated the search for a new Ru-based superconductor
the paramagnetic state at an electronic temperature
and gave rise to interest in the investigation of the elec-
β = 20eV-1 (580K).
tronic and magnetic properties of ruthenates. Synthesis
Local spin-spin correlation function 〈Sz(τ)Sz(0)〉 on
and study of a complete series of Ca2-xSrxRuO4 alloys
the imaginary time axis characterizes the lifetime of the
with isoelectronic substitution of Sr2+ by smaller Ca2+
local moment. If the magnetic moments are localized,
ion was performed by Nakatsuji and Maeno [3, 4]. At
this correlation function is constant: 〈Sz (τ)Sz (0)〉 ≈ S2
concentration x = 0.5 the susceptibility shows a Curie
and the imaginary time dependence of this correlation
form with a S = 1/2 moment (not S = 1) per Ru ion
function indicates the delocalization of spin moments,
and the alloy exhibits metallic transport properties. At
which is the Fermi liquid regime. The real part of the
higher concentrations of Sr, Ca2-xSrxRuO4 has a para-
local spin-spin correlation function on the real frequency
magnetic metallic state. At a higher Ca concentration,
axis can be used to characterize the degree of local-
the alloy remains metallic, but with AFM fluctuations
ization: the half-width of 〈Sz(ω)Sz (0)〉 peak at a half-
at low temperatures. With a further increase in Ca con-
height is in inverse proportion to the lifetime of the local
centration (x < 0.2), the alloy becomes an insulator.
moment [14].
To describe the evolution of the electronic struc-
The local spin-spin correlation functions
ture at intermediate concentration, the orbital selective
〈Sz(ω)Sz (0)〉 for different x are shown in Fig. 1
Mott transition model was proposed [5]. In this model
(upper panel). For x = 2 the peaks of t2g dxy and dxz,yz
t2g manifold is divided into two groups of orbitals: de-
generate xz,yz-orbitals and in-plane xy-orbital strongly
π-hybridized with oxygen 2p-orbitals. Using LDA re-
sults as input parameters for the DMFT method within
the NCA computation scheme [6] the authors obtained
orbital-selective behavior: the appearance of Mott local-
ization in (xz, yz) subbands, while the broader half-filled
xy-band remains itinerant.
In the present paper the DFT + DMFT method
was applied to study the electronic structure of
Ca2-xSrxRuO4
[7,
8]. The non-interacting band
structure was calculated using the GGA (generalized
gradient approximation) [9] as implemented in the
Quantum Espresso package [10]. An effective Hamilto-
nian was constructed using the basis of atomic-centered
Fig. 1. (Color online) Local spin-spin correlation func-
Wannier functions as described in [11]. The DMFT im-
tion Ca2-xSrxRuO4 calculated within DFT + DMFT at
purity problem was solved by hybridization expansion
β = 20 U = 1.5eV and JH = 0.7eV for x = 0, 0.5 and 2.0
on imaginary time axis (lower panels) and real frequencies
1)e-mail: shorikov@imp.uran.ru
(upper panels)
Письма в ЖЭТФ том 116 вып. 11 - 12
2022
777
3∗
778
A. O. Shorikov, D. Y. Novoselov, D. M. Korotin, V. I. Anisimov
orbitals have almost equal width and shape which is
Education of the Russian Federation (theme “Elec-
consistent with small distortion of oxygen octahedra
tron” # 122021000039-4). DMFT calculations were sup-
in Sr2RuO4. The broad local spin-spin correlation
ported by the Russian Science Foundation (Project
functions correspond to a metallic phase with weakly
19-12-00012).
localized electrons. On the other hand, in the case
This is an excerpt of the article “Orbital selective
of Ca2RuO4 (x = 0) the peaks become sharp and
localization enhancement in Ca2-xSrxRuO4”. Full text
the width reduces by a factor ≈ 2. The 〈Sz(τ)Sz (0)〉
of the paper is published in JETP Letters journal.
correlator has substantial value in the whole range
DOI: 10.1134/S0021364022602391
[0, β] as well as lifting of degeneracy of dxz,yz orbitals
due to strong distortion of crystal structure. One can
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P. Giannozzi, S. Baroni, N. Bonini et al. (Collaboration),
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13.
“AMULET” http://amulet-code.org.
is regulated by average Coulomb interaction value.
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assignment of the Ministry of Science and Higher
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Письма в ЖЭТФ том 116 вып. 11 - 12
2022