Condensed Matter Theory and Computation

The PhD project will be carried out in collaboration with the computational theoretical group of Prof. Marco Govoni and with experimental groups working on quantum materials and spin defects. The research will focus on the theoretical and computational investigation of spin–phonon interactions and their role in spin relaxation and decoherence in solid-state systems.

The project aims at predicting the spin relaxation time (T₁) and the spin coherence time (T₂), key figures of merit for color centers and spin defects in quantum technologies. T₁ describes energy exchange with the environment, whereas T₂ quantifies the loss of phase coherence; both are critical for applications in quantum sensing, communication, and information processing. Spin–phonon coupling is traditionally associated with T₁; its role in limiting T₂ will be explicitly investigated.

The activity will combine methodological development with large-scale simulations based on first-principles electronic-structure methods and atomistic modeling. A central goal is the development of predictive computational frameworks to describe spin–phonon coupling and spin dynamics in realistic materials. This will include an explicit treatment of nuclear dynamics, accounting for anharmonic effects beyond the harmonic approximation.

Spin–phonon interactions will be addressed using non-perturbative approaches, enabling the description of multiphonon processes and their impact on both relaxation and pure dephasing. The project will benefit from close interactions between theory and experiments, enabling comparison with spectroscopic and spin-coherence measurements on candidate quantum materials.

The study of anharmonic and quantum contributions to nuclear dynamics is central to understanding a broad class of phenomena, from the phase diagram of water to near roomtemperature metal hydride superconductors, and has important theoretical and technological implications [1].

Positive antimuons in muon spin relaxation spectroscopy (muSR) act as a light analogue of the proton (mass ≈ 1/9 of a proton). As a result, muons exhibit amplified anharmonic and quantum dynamical effects, making muSR a powerful probe of lightnuclei dynamics and of the crossover between diffusion regimes, from quantum delocalization to classical over-the-barrier hopping [2].

Experimentally, muon spectroscopy is on the verge of a step change: recent advances in positionsensitive particle detectors are expected to increase measurement accuracy by one to two orders of magnitude [3]. Advanced theoretical modeling will be essential to interpret the unprecedented resolution of experimental data from the new beamlines, to keep pace with the increased count rate, and to link intrinsic electronic structure to features in experimental data that were previously obscured by limited count rates.

This PhD project will contribute on two fronts: (i) develop theoretical models and simulation tools to describe quantum and anharmonic effects in the motion of light particles in solids, and to explore the crossover from coherent tunneling to classical diffusion; and (ii) establish analysis frameworks to interpret forthcoming highprecision muonic measurements and support spectroscopic data analysis [4].

The research will be carried out within an established international collaboration involving largescale facilities at the Paul Scherrer Institute (Switzerland) and the ISIS Neutron and Muon Source (UK).

References:
[1] Joseph A. Morrone and Roberto Car “Nuclear Quantum Effects in Water”, Phys. Rev. Lett. 101, 017801 (2008); Thomas E. Markland and Michele Ceriotti, “Nuclear quantum effects enter the mainstream”, Nat. Rev. Chem. 2, 0109 (2018); Ion Errea, et al. “Quantum crystal structure in the 250-kelvin superconducting lanthanum hydride”, Nature 578, 66 (2020).
[2] R. Kadono et al “Quantum diffusion of positive muons in copper”, Phys. Rev. B 39, 23 (1989); M. Camani et al, “Positive Muons in Copper: Detection of an Electric-Field Gradient at the Neighbor Cu Nuclei and Determination of the Site of Localization” Phys. Rev. Lett. 39, 836 (1977); T. U. Ito and R. Kadono “Distinguishing Ion Dynamics from Muon Diffusion in Muon Spin Relaxation” J. Phys. Soc. Jpn. 93, 044602 (2024).
[3] H. Augustin et al, “New Frontiers in Muon-Spin Spectroscopy Using Si-Pixel Detectors”, arXiv:2504.12993.
[4] S. J. Blundell and T. Lancaster, “DFT + μ: Density functional theory for muon site determination” Appl. Phys. Rev. 10, 021316 (2023); I. J. Onuorah et al “Automated computational workflows for muon spin spectroscopy”, Digital Discovery 4, 523 (2025).

Atomically thin materials are opening a new frontier in condensed-matter physics, where reducing a crystal to a single layer can reveal entirely new phenomena. In two dimensions, magnetism becomes both richer and more tunable: exotic phases such as the Berezinskii–Kosterlitz–Thouless state can emerge, while magnetic properties can be controlled through electric fields, doping, and stacking. Particularly exciting is the recent discovery of altermagnets, a new class of magnetic materials with unique spin properties and strong potential for next-generation spintronics.
At the same time, 2D materials can host topological phases of matter, including the quantum spin Hall and anomalous Hall states, enabling dissipationless electronic transport and novel quantum functionalities. Their true versatility appears when individual monolayers are assembled into van der Waals heterostructures, where interactions between layers generate emergent properties absent in the parent compounds. Reduced dimensionality and interlayer coupling also strongly modify electron–phonon interactions, offering additional routes to engineer material behavior.
Possible research directions in this area combine advanced atomistic simulations, algorithm development, and materials discovery to predict and characterize novel magnetic and topological 2D systems for applications in spintronics and valleytronics. Projects are carried out in close collaboration with leading theoretical and experimental groups, including EPFL, Cambridge, SISSA, CNRS Montpellier, and the University of Geneva.

References:
[1] A Marrazzo and M. Gibertini, npj 2D Materials and Applications 6, 30 (2022)
[2] M. Gibertini et al, Nature Nanotechnology 14, 1116 (2019)
[3] F. Yao et al, Nature Nanotechnology 20, 609 (2025)
[4] S. Poncé et al., Phys. Rev. Lett. 130, 166301 (2023)

This PhD theme focuses on the development and application of predictive atomistic and quantum-mechanical modelling strategies for nanostructures and functional materials. The emphasis is on physically grounded simulations, where machine learning (ML) is leveraged to access electronic, electrostatic and transport properties that are difficult to compute directly at large scales. The broader goal is to train a PhD student in modern computational materials physics, combining electronic-structure theory, statistical mechanics, atomistic modelling and selected machine-learning techniques to predict experimentally relevant observables in complex materials.
Two doctoral research projects are proposed:
1. Electronic and electrostatic properties of nanostructures beyond machine-learning potentials.
This line will address the prediction of quantities such as charge densities, electrostatic potentials, density of states and local density of states, with direct relevance for the interpretation of scanning tunneling microscopy and spectroscopy. Physics-informed ML models may be used to reconstruct electronic observables in complex nanostructures, interfaces and defective systems, and to assess the impact of long-range electrostatics on transport properties, including in ionic liquids and superionic conductors. 
2. Anharmonic and quantum effects in vibrational properties and heat transport.
This line will investigate the role of lattice anharmonicity, quantum nuclear effects and non-perturbative phonon physics in the thermal conductivity of materials of technological relevance (such as, eg., cubic boron arsenide). The project may combine first-principles calculations, Boltzmann transport approaches and advanced methods such as the stochastic self-consistent harmonic approximation to obtain effective interatomic force constants and describe regimes where standard perturbative treatments become insufficient.

Main collaborations @ UNIMORE:
R. Bianco, G. Goldoni, M. Govoni, E. Molinari, A. Ruini

Main collaborations @ CNR-NANO:
D. Prezzi

Main external collaborations:
SISSA: S. Baroni, S. de Gironcoli, A. Marrazzo — Sorbonne Université: A. Grisafi — EPFL: M. Ceriotti — TU Delft: K. Rossi — RBI Zagreb: I. Lončarić

Both excitons and plasmons are collective, neutral excitations of solids that arise as a consequence of the long range of Coulomb forces. Whereas excitons are traditionally investigated in semiconductors and plasmons in metals, the monolayer semimetal WTe 2 provides a novel playground for exotic, hybrid excitations. At charge neutrality the system is thought to be an “excitonic insulator”, the long-sought stable Bose-Einstein condensate of excitons [1]. Amazingly, it becomes an unconventional superconductor with an ultra-tiny amount of electron doping [2]. The proximity of these two phases reminds us of the long-standing puzzle of high-T c superconductivity [3]. In order to clarify the underlying physics, we will investigate the excitons and plasmons of the ‘normal’ phase of monolayer WTe 2 , as a function of electron doping, hunting for mode softening and long-lived excitations. We will tackle the computational challenge of deriving the collective excitations through accurate many-body perturbation theory from first principles, as well as rely on a complementary model approach to grasp the essential phenomena.

This work is planned within the wider framework of collaborative research with the quantum transport group at Univ Washington, Seattle (D Cobden).

Collaborations: David Cobden (Univ Washington, Seattle), James McIver (Univ Columbia, New York), Hope Bretscher (Boston College, Chestnut Hill).

References:
[1] B Sun, W Zhao, T Palomaki, Z Fei, E Runburg, P Malinowski, X Huang, J Cenker, Y-T Cui, J-H Chu, X Xu, SS Ataei, D Varsano, M Palummo, E Molinari, M Rontani, DH Cobden, Evidence for equilibrium exciton condensation in monolayer WTe 2 , Nature Physics 18, 87 (2022).
[2] E Sajadi et al, Gate-Induced Superconductivity in a Monolayer Topological Insulator. Science 362, 922 (2018).
[3] T Song et al, Unconventional Superconducting Quantum Criticality in Monolayer WTe 2 , Nature Physics 20, 269 (2024).

The in silico design of materials with desired functionalities for future technologies is developing enormously thanks to the rapid evolution of high-performance computing, data analysis and ML, combined with increasingly predictive methods for the study of fundamental properties. The integration of these components is crucial to accelerate the discovery of new materials in view of the ecological transition. In this context, we propose two PhD projects:

[1] Ab initio spectroscopies for interfaces/interphases in next-generation battery materials The project involves the development/use of automated protocols for calculating in-operando core level and vibrational spectra from first principles, focusing on interfaces and interphases in Li-based batteries and beyond. Objectives include combining direct calculations of spectra with advanced schemes based on local topologies and bond graphs and ML surrogate models based on density-related descriptors. The challenging inverse problem of generating structures from spectra will also be investigated. Outcomes include comprehensive atlases of spectroscopic fingerprints, advanced methods for spectral prediction and battery optimization.

[2] Design of materials with enhanced thermoelectric performance Thermoelectric materials play a crucial role in energy harvesting applications by converting waste heat into electricity and back. The device efficiency depends on intricate electron/phonon interactions: the evaluation of the thermoelectric figure-of-merit is challenging. We here aim to contribute to the advancement of atomistic simulations in this field, by implementating a greatly accelerated approach to evaluate anharmonic constants via ML interatomic potentials trained over short ab-initio MD trajectories. Final goal is the computational design of novel semiconductor quantum wires with superior thermoelectric performance.

Students interested in these specific proposals, or more generally in these research topics, are encouraged to get in touch for further information and discussion at alice.ruini@unimore.it

Main collaboration/co-tutors:
Federico Grasselli (FIM) [1,2], Dr. Deborah Prezzi (CNR-NANO) [1], Francesco Rossella (FIM) [2], Dr. Pino D’Amico (CNR-NANO) [2] + several coworkers from national and international colleborations, also in the framework of funded projects

References:
R Maji et al, “Insights into the stability and reactivity of lithiated Si-binder interfaces for next generation lithium-ion batteries”, Journal of Power Sources 610, 234705 (2024)
V.A. Bastos et al, “Ab initio study of saddle-point excitons in monolayer SnS₂”, Phys. Rev. B in press (2026)
M. Isram et al, “Impact of Mg Doping on Structural, Morphological and Thermoelectric Properties of SnO2 Nanoparticles: A Combined Experimental-Theoretical Investigation”, Molecules 30, 4135 (2025)