Pis’ma v ZhETF, vol. 111, iss. 8, pp. 524 - 525

April 25

Tuning of electronic and vibrational properties of transition metal

selenides TSe₂ (T = Os, Ru) and their metallization under high pressure

P. G. Naumov^+∗, A. O. Baskakov^∗1), S. S. Starchikov^∗, I. S. Lyubutin^∗, Yu. L. Ogarkova^∗, M. V. Lyubutina^∗,

O.I.Barkalov^×, S.A.Medvedev⁺

⁺Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany

^∗Shubnikov Institute of Crystallography of Federal Scientific Research Centre

“Crystallography and Photonics” of Russian Academy of Sciences, 119333 Moscow, Russia

^×Institute of Solid State Physics, Russian Academy of Sciences, 142432 Chernogolovka, Russia

Submitted 27 March 2020

Resubmitted 27 March 2020

Accepted 29

March 2020

DOI: 10.31857/S123456782008008X

In recent decades, considerable interest has been fo-

pressure in NiSe₂, the sample remains a normal non-

cused on the structural, electronic, optical, and chemical

superconducting metal. Some correlations can also be

properties of transition metal dichalcogenides (TMDs)

expected between the pyrite-type structure of TMDs

TX₂ (T is a transition metal cation and X is a chalco-

and the appearance of a superconducting state. In this

gen anion) [1-6]. The weak van der Waals bonding [1]

direction, it is interesting to study and compare the

between the two-dimensional TMDs atomic layers al-

transport properties and phonon modes of osmium dis-

lows the formation of various low-dimensional struc-

elenide OsSe₂ and ruthenium diselenide RuSe₂ under

tures that can compete with graphene in important

high-pressure conditions.

technical applications, including nanoelectronics, pho-

In our studies monocrystalline OsSe₂ and RuSe₂

tonics and energy storage [7, 8]. In this case, TMDs ex-

samples were synthesized by the chemical vapor trans-

hibit a significant variety of electronic properties [1].

port method. The stoichiometry of the obtained crystals

OsSe₂ is a diamagnetic semi-metal with a pyrite-type

was proved using energy dispersive X-ray spectroscopy.

structure [9, 10]. RuSe₂ is a diamagnetic semiconductor

A screw-clamped diamond anvil cell equipped with 550-

with an indirect band gap at ambient pressure [11, 12].

µm culet diamond anvils was used for the simultaneous

In recent studies of superconductivity in TMD with a

Raman spectroscopy and electrical resistivity measure-

pyrite-type structure, the relationship between super-

ments at high pressure up to 43 GPa.

conductivity and structural instability, which involves

Raman spectroscopy measurements were performed

the destabilization of anionic dimers, has often been

to study the evolution of the vibrational properties of

discussed. In PdSe₂, such destabilization is caused by

OsSe₂ and RuSe₂ under high pressure. Weakening of Se-

the application of external pressure [13], and in IrSe₂

Se chemical bonds in OsSe₂ and RuSe₂ samples under

by Rh doping [14]. This kind of structural instability

high pressure was not observed, which is confirmed by a

leads to a decrease in the frequency of the stretch-

constant increase in the frequency of the A_g mode with

ing A_g Se-Se mode due to an increase in the length

pressure in both compounds.

of the Se-Se bond, as demonstrated by Raman spec-

Moreover, our Raman spectroscopy studies did not

troscopy.

reveal any indication of structural phase transitions up

However, for the PdS₂ and NiSe₂ dichalcogenides

to pressures of about 40 GPa. Thus, it can be assumed

with a pyrite-type structure, it was shown that the

that the pyrite-type structure remains stable up to the

destabilization of anionic dimers is not necessary for

highest pressures attained in the experiments.

the occurrence of superconductivity, and such desta-

We also performed electrical transport measure-

bilization is not a sufficient condition for the for-

ments to detect electronic transitions under applied

mation of superconductivity [15]. Therefore, in PdS₂

pressure in OsSe₂ and RuSe₂ samples. It turned out

there is no correlation between the softening of the S-

that the resistivity of both samples at room tempera-

S dumbbell bonds and the dependence T_c(P ). Mean-

ture decreases with increasing applied pressure (Fig. 1).

while, despite the elongation of Se-Se bonds under

The similar effects reported in [13, 15] were associated

with a substantial overlapping of the conduction and

¹⁾e-mail: arseniybaskakov@gmail.com

valence bands.

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Tuning of electronic and vibrational properties of transition metal selenides . . .

525

tion of semimetal into metal under pressure. An increase

in the T_c critical temperature with pressure was found

for both samples. OsSe₂ demonstrated the classic dome-

shape behavior of T_c(P ) dependence, while for RuSe₂,

the T_c remains constant above 35 GPa. For both ma-

terials, no indications of a structural phase transition

were found in our spectroscopic studies up to the high-

est pressures.

The work on preparation of the high-pressure cells,

loading of high-pressure cells, Raman and transport

measurements at high pressures, analysis and processing

of the results of these measurements, and preparation of

the manuscript was supported by the Russian Science

Foundation (project # 17-72-20200). The sample char-

acterization was supported by the Ministry of Science

and Higher Education of the Russian Federation within

the State assignment FSRC “Crystallography and Pho-

tonics” Russian Academy of Sciences.

Full text of the paper is published in JETP Letters

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