Doctor of physics and mathematics, professor at the Department of Theoretical Physics and Quantum Technologies, senior researcher at the Landau Institute for Theoretical Physics

Research interests

*Condensed matter physics: electronic properties of low-dimensional and strongly anisotropic conductors, magnetic quantum oscillations in metals, magnetoresistance (especially in strongly anisotropic conductors), charge- or spin-density waves, strongly interacting electronic systems and highly fermionic states, organic metals and superconductors, superconductivity against the background of charge/spin-density waves, high-temperature superconductors, liquid helium surface structure and surface quantum states of particles (electrons, ions, neutrons, clusters) in its vicinity.*

*Neutron spectroscopy devices: neuron beam focusing with the moving heterogeneous magnetic field. Neuron traps at the liquid helium surface.*

*Quantum calculations and quantum computer design: application of electronic and ionic related states at the liquid helium surface for the implementation of the quantum bit system.*

Field of knowledge according to OECD

*Condensed matter physics*

##### Doctor of physics and mathematics

2015: defending the doctoral thesis entitled “Special aspects of magnetoresistance in layered quasi two-dimensional conductors” majoring in theoretical physics. Diploma of doctor of physics and mathematics DND No. 001784.

2002: defending his PhD thesis at the University of Konstanz, Germany, under the supervision of professor Peter Wyder. Grade: excellent (Magna Cum Laude). Thesis topic: “Magnetic quantum oscillations in quasi-2D metals”. Electronic copy of thesis.

2001: defending his thesis entitled “Two-dimensional electronic gas on the surface of liquid helium”, diploma of PhD in physics and mathematics majoring in theoretical physics No. KT 061685.

1998: Master’s degree diploma (cum laude: 100% excellent grades) and physical engineer diploma majoring in general and applied physics.

1996: Bachelor’s degree diploma (cum laude: >98% excellent grades).

1992: graduated from school with honors.

##### Professor at the Department of Theoretical Physics and Quantum Technologies, senior researcher at the Landau Institute for Theoretical Physics

2015 — present: professor (part-time) at the Department of Theoretical Physics and Quantum Technologies at NUST MISIS. Lecture courses on the theory of metals ans quantum solid state physics.

2016 — present: senior researcher at the Landau Institute for Theoretical Physics of the Russian Academy of Sciences.

##### Main results of scientific work

The key area of academic interests is about electronic properties of strongly anisotropic conductors that cover all high-temperature superconductors under the atmospheric pressure, heterostructures, organic metals and many other compounds. The following academic results were obtained in this area:

- Magnetoresistance and quantum oscillations.
- For the first time, the theory of magnetoresistance in strongly anisotropic conductors [Phys. Rev. B 67, 144401 (2003); Phys. Rev. B 98, 045118 (2018)] was developed, where the integral of the interlayer electronic transaction is comparable to, or falls below, the cyclotron energy. To that extent, the traditional theory for ordinary metals becomes inapplicable, and new qualitative effects occur. Through the use of this theory, the so-called slow (or differential) magnetic oscillations [Phys. Rev. Lett. 89, 126802 (2002)] with the frequency determined by the integral of transition (rather than the cross-sectional area of the Fermi surface) that survive up to higher temperatures and are more resistant to the sample heterogeneities and are, therefore, easier observed in experiments were explained and described for the first time. This effect remained a mystery for several decades and allowed determining the interlayer transition integral and the disorder type using experimental magnetoresistance data in various layered conductors. This theory explains the shift in the quantum conductivity oscillations beating phase as compared to magnetizability [Phys. Rev. B 65, 060403
^{®}(2002)] and other thermodynamic values. - The mutual impact of angular and quantum magnetoresistance oscillations [Phys. Rev. B 90, 115138 (2014); Phys. Rev. B 95, 195130 (2017)] was analyzed. The relevant general formulae convenient for analysis with experimental data were generated.
- The strong longitudinal interlayer magnetoresistance in quasi two-dimensional metals [Phys. Rev. B 83, 245129 (2011); Phys. Rev. B 88, 054415 (2013)] having the core dependence in a strong magnetic field was predicted. This important and sudden effect was confirmed by us through experiments [Phys. Rev. B 86, 165125 (2012)] and is omitted from the standard theory based on tau approximation. Its description makes use of the Feynman diagram.
- It was demonstrated that magnetic oscillations in cuprate high-temperature superconductors of the YBCO family may be explained by the spectrum split due to the interlayer electron transition, rather than by small pockets of the Fermi surface [Phys. Rev. B 96, 165110 (2017)]. Its explains an unusual harmonic composition of oscillations and removes inconsistencies between data on ARPES and magnetic oscillations published in dozens of articles in the Nature journal. This paper was included in the key achievements of the Institut Laue-Langevin in France for 2017.
- Through the use of symmetry arguments, it was demonstrated [npj Quantum Materials 6, 11 (2021)] that the effective g-factor of charge carriers in many metals with the antiferromagnetic alignment measured by its magnetic quantum oscillations equals zero. The experimental research of this effect is conducted in several compounds and compared with the proposed theory. We have discovered that the antiferromagnetic state of layered organic conductor κ-(BETS)2FeBr4 does not show the Shubnikov-de Haas spin-based oscillation modulation, as opposed to the paramagnetic state of the same material. It evidences the degeneration of the Landau levels by spin predicted for antiferromagnetic conductors. Similarly, we do not see any spin-based modulation in the angular dependence of slow Shubnikov-de Haas oscillations in the Nd2−xCexCuO4 cuprate optimally compounded by electrons. It indicates the existence of the Neel wall in this superconductor even with the optimal compounding.

- For the first time, the theory of magnetoresistance in strongly anisotropic conductors [Phys. Rev. B 67, 144401 (2003); Phys. Rev. B 98, 045118 (2018)] was developed, where the integral of the interlayer electronic transaction is comparable to, or falls below, the cyclotron energy. To that extent, the traditional theory for ordinary metals becomes inapplicable, and new qualitative effects occur. Through the use of this theory, the so-called slow (or differential) magnetic oscillations [Phys. Rev. Lett. 89, 126802 (2002)] with the frequency determined by the integral of transition (rather than the cross-sectional area of the Fermi surface) that survive up to higher temperatures and are more resistant to the sample heterogeneities and are, therefore, easier observed in experiments were explained and described for the first time. This effect remained a mystery for several decades and allowed determining the interlayer transition integral and the disorder type using experimental magnetoresistance data in various layered conductors. This theory explains the shift in the quantum conductivity oscillations beating phase as compared to magnetizability [Phys. Rev. B 65, 060403
- Anisotropic conductors are often unstable to the generation of waves of charge or spin density that competes with superconductivity. The following results were obtained in this area:
- It was demonstrated for the first time [Phys. Rev. B 95, 165120 (2017); JETP Lett. 105, 786 (2017); Phys. Rev. B 98, 014515 (2018)] that the emerging superconductivity in the form of isolated islands results in anisotropic changes to conductivity and provides information regarding the volumetric share and form of superconductive islands. We applied this method to the analysis of experimental data in high-temperature superconductor FeSe and determined the temperature dependence of the volumetric share of superconductive islands. We observe a good qualitative consent for the temperature dependence of the superconductive phase share determined by the diamagnetic response and by the altered conductivity anisotropy based on the proposed model, which emphasizes its correctness for the qualitative and even quantitative description of this effect. The anisotropy of the superconductive transition itself was also explained [Phys. Rev. B 103, 014519 (2021)].
- The method of nonperturbative recording of impact of a charge/spin density wave covering only a portion of the Fermi surface on the remaining electronic states was developed. With the use of this method, the impact of density on superconductivity of layered materials was examined, and a number of unusual superconductivity properties against the density wave was obtained [Phys. Rev. B 75, 020507
^{®}(2007); Phys. Rev. B 77, 224508 (2008)] . In particular, a significant increase of the upper critical field with the unchanged Tc observed in layered organic metals was explained. - It was demonstrated that changing the conductivity anisotropy upon the transition to the state with the charge density wave provides helpful information regarding its electronic structure, in particular, regarding the order parameter anisotropy [Phys. Rev. Lett. 112, 036601 (2014)].
- The phase diagram of charge density waves in a magnetic field for a difference electron dispersion law (for example, see the following papers [Phys. Rev. B 72, 195106 (2005); Phys. Rev. B 68, 201101
^{®}(2003)]) was examined. Specifically, a cascade of phase transitions between states with the different nesting (density wave) vector quantum with the magnetic field slope arising from the competition of the orbital and spin-based magnetic field impact on conductive electrons was proposed and examined.

- Liquid helium surface.
- A new type of excitations at the liquid helium surface [Letters to the Journal of Experimental and Theoretical Physics 78, 935 (2003), Letters to the Journal of Experimental and Theoretical Physics 87, 114 (2008), the Journal of Experimental and Theoretical Physics, 133, 370 (2008), J. Low Temp. Phys. 163, 131 (2011)] representing atoms at the surface quantum level was proposed and examined. It was demonstrated [Journal of Experimental and Theoretical Physics 155, 338 (2019)] that the experimental data on inelastic scattering of neutrons on a thin helium film and numeric computations is in line with this prediction.
- The temperature dependence of the scattering speed of ultracold neutrons on the liquid helium surface on steam atoms and ripplons — quanta of surface waves was examined in theory [Phys. Rev. C 94, 025504 (2016)]. The latter turned to be decisive at the temperature below 0.5К and linear at the tempetarure of T. Therefore, it should be taken into account even with the lowest temperature for the exact determination of the lifetime of neutrons with the use of liquid helium traps.
- The properties of negative large-sized ions (low coupled energy) on the liquid helium surface were proposed and examined [Journal of Experimental and Theoretical Physics, 115, 593 (1999)]. It was shown that such ions are held on the surface and may be helpful for the experimental implementation of quantum bits with a long decoherence period. It was demonstrated that negative ions that are not stable in the vacuum may be implemented on the liquid helium surface.

Scopus Hirsch Index — 16.

Number of articles on Scopus — 89.

ORCID: 0000-0002-4125- 1215.

ResearcherID: R-9909-2016.

Scopus AuthorID: 7004467795.

##### Significant research projects, grants

Federal Target Program of the Ministry of Education and Science “Scientific and pedagogical personnel of Russia”,

Presidential grants for young scientists:

- MK-429.2003.02
(2003-2005); - MK-4105.2007.02
(2007-2008); - МК-2320.2009.2
(2009-2010).

Dynasty Foundation Grant

Grant from the Foundation for the Development of Theoretical Physics and Mathematics “Basis”

RFBR No. 19-02- 01000

##### Significant publications

- R. Ramazashvili, P.D. Grigoriev, T. Helm, F. Kollmannsberger, M. Kunz, W. Biberacher, E. Kampert, H. Fujiwara, A. Erb, J. Wosnitza, R. Gross, M.V. Kartsovnik,
*Experimental evidence for Zeeman spin—orbit coupling in layered antiferromagnetic conductors*, npj Quantum Materials 6, 11 (2021) - P.D. Grigoriev, A.A. Sinchenko, P.A. Vorobyev, A. Hadj-Azzem, P. Lejay, A. Bosak, P. Monceau,
*Interplay between band crossing and charge density wave instabilities*, Phys. Rev. B 100, 081109^{®}(2019). - S.S. Seidov, K.K. Kesharpu, P.I. Karpov, P.D. Grigoriev,
*Conductivity of anisotropic inhomogeneous superconductors above the critical temperature*, Phys. Rev. B 98, 014515 (2018). - T.I. Mogilyuk, P.D. Grigoriev,
*Magnetic oscillations of in-plane conductivity in quasi-two-dimensional metals*, Phys. Rev. B 98, 045118 (2018). - P.D. Grigoriev, T.I. Mogilyuk,
*False spin zeros in the angular dependence of magnetic quantum oscillations in quasi-two-dimensional metals*, Phys. Rev. B 95, 195130 (2017). - P.D. Grigoriev, T. Ziman,
*Magnetic oscillations measure interlayer coupling in cuprate superconductors*, Phys. Rev. B 96, 165110 (2017). - A.A. Sinchenko, P.D. Grigoriev, P. Lejay, P. Monceau,
*Spontaneous Breaking of Isotropy Observed in the Electronic Transport of Rare-Earth Tritellurides*, Phys. Rev. Lett. 112, 036601 (2014). - P.D. Grigoriev,
*Longitudinal interlayer magnetoresistance in strongly anisotropic quasi-two-dimensional metals*, Phys. Rev. B 88, 054415 (2013). - P.D. Grigoriev, M.V. Kartsovnik, W. Biberacher,
*Magnetic-field-induced dimensional crossover in the organic metal**α**-(BEDT-TTF)**2**KHg(SCN)**4*, Phys. Rev. B 86, 165125 (2012) . - P.D. Grigoriev,
*Weakly incoherent regime of interlayer conductivity in a magnetic field*, Phys. Rev. B 83, 245129 (2011)]. - P.D. Grigoriev,
*Properties of superconductivity on a density wave background with small ungapped Fermi surface parts*, Phys. Rev. B 77, 224508 (2008). - L.P. Gor’kov, P.D. Grigoriev,
*Nature of superconducting state in the new phase in (TMTSF)**2**PF**6**under pressure*, Phys. Rev. B 75, 020507^{®}(2007). - P.D. Grigoriev, D.S. Lyubshin,
*Phase diagram and structure of the charge-density-wave state in a high magnetic field in quasi-one-dimensional materials: A mean-field approach*, Phys. Rev. B 72, 195106 (2005) . - P.D. Grigoriev,
*Theory of the Shubnikov-de Haas effect in quasi-two-dimensional metals*, Phys. Rev. B 67, 144401 (2003) . - P.D. Grigoriev, M.V. Kartsovnik, W. Biberacher, N.D. Kushch, P. Wyder,
*Anomalous beating phase of the oscillating interlayer magnetoresistance in layered metals*, Phys. Rev. B 65, 060403^{®}(2002) . - M.V. Kartsovnik, P.D. Grigoriev, W. Biberacher, N.D. Kushch, P. Wyder,
*Slow oscillations of magnetoresistance in quasi-two-dimensional metals*, Phys. Rev. Lett. 89, 126802 (2002).

##### Scientific supervision and teaching

- T.I. Mogilyuk T.I. “Magnetic quantum and angular oscillations of conductivity in layered metals”, PhD in physics and mathematics obtained on 03/23/2021 at MIPT.
- P.A. Vorobyev. “Influence of the charge density wave on the electronic properties of rare-earth tritellurides”, Master’s degree, obtained on 05/23/2019 at the Moscow State University.
- K.K. Kesharpu K.K. “Temperature dependence of resistivity at the transition to a charge-density-wave State in rare-earth tritellurides ”, Master’s degree obtained in June 2017 at NUST MISIS.
- I.A. Kolesnikov. “Investigation of the anisotropic effect of incipient superconductivity on electron transport in iron selenide”, Master’s degree obtained in June 2020 at NUST MISIS.
- Aset Hamzauli. “Estimation of the frequency of magnetic quantum oscillations in high-temperature superconductors of the YBaCuO family in various scenarios”, Master’s degree obtained in June 2019 at NUST MISIS.

Currently: supervision over 2 postgraduates and 1 Master’s degree student at NUST MISIS.

##### Teaching

Annual course of lectures “Quantum solid state physics” in Russian-language and English-language Master’s programs, and a semester course of lectures “Condensed-matter physics” for graduate students at the Department of Theoretical Physics and Quantum Technologies (TPQT) of NUST MISIS.

##### Scientific and social activities

Participation in dissertation councils at NUST MISIS.