B4 Research Projects 2025
(Krüger Group)Project 1: ARPES calculation of altermagnetic surfaces
Background. Altermagnets [1,2] are a new type of magnetic structures. Similar to "normal" antiferromagnets, they have two collinear magnetic sublattices one with spin-up and one with spin down, such that the total magnetization is zero. However, contrary to usual antiferromagnets the two sublattices are not connected by a crystal translation, but by a rotation. As a consequence, certain band states are spin-polarized (which is impossible for normal antiferromagnets). This property opens up many interesting technological applications for altermagnets. The experimental evidence for spin-polarized band states is angle-resolved photoemission spectroscopy (ARPES) [3]. The aim of this project is to calculate using density functionat theory (DFT) and the "SPR-KKR"[4] code: (i) the bulk and surface electronic and magnetic structure (ii) ARPES spectra and compare with available experiments.Tasks
1. Search the literature for interesting altermagnetic "candidate materials"
2. Learn DFT and the SPRKKR code.
3. Bulk electronic structure calculation. Confirm altermagnetic state and find spin-polarized bands.
4. Build surface model and compute surface electronic structure
5. Calculate ARPES
[1] Altermagnetism (wikipedia)
[2] Libor Šmejkal, Jairo Sinova, and Tomas Jungwirth, Emerging Research Landscape of Altermagnetism, Phys. Rev. X 12, 040501 (2022).
[3] J. Krempaský et al. Altermagnetic lifting of Kramers spin degeneracy. Nature 626, 517–522 (2024).
[4] Munich SPR-KKR code
Project 2: Resonant photoelectron diffraction of altermagnet candidate material RuO2
Background. Altermagnets are a new type of magnetic structures (see project 1). Ruthenium oxide (RuO2) was one of the first candidate materials [1], but to date, it is still not clear whether RuO2 is altermagnetic or non-magnetic [2]. Krüger has proposed a new method for measuring the local magnetic moments of altermagnets using the circular dichroism (CD) in resonant photoelectron diffraction RPED [3]. The aim of this study is to compute CD-RPED for RuO2 in both non-magnetic and altermagnetic ground state in order to confirm whether RuO2 is altermagnetic or not.Tasks
1. Compute the electronic structure of RuO2 using DFT+U and the VASP code
2. Build a crystal field model for RuO2 and learn the RPED code developed by Krüger.
3. Compute the CD-RPED pattern for RuO2 in both non-magnetic and altermagnetic ground state
[1] O. Fedchenko et al. Observation of time-reversal symmetry breaking in the band structure of altermagnetic RuO2. Sci.Adv.10,eadj4883(2024)
[2] P. Kessler et al. Absence of magnetic order in RuO2: insights from μSR spectroscopy and neutron diffraction. npj Spintronics 2, 50 (2024).
[3] P. Krüger, Circular dichroism in resonant photoelectron diffraction as a direct probe of sublattice magnetization in altermagnets. arXiv:2504.08380 (2025)
Project 3: Electronic structure and resonant photoelectron diffraction of altermagnet candidate material Mn5Si3
Background. Altermagnets are a new type of magnetic structures (see project 1). Mn5Si3 has been identified as a possible altermagnet [1,2], but direct experimental evidence of the magnetic structure is missing. Krüger has proposed a new method for measuring the local magnetic moments of altermagnets using the circular dichroism (CD) in resonant photoelectron diffraction RPED [3]. The aim of this study is to find the magnetic ground state of Mn5Si3 using DFT or DFT+U calculations and then compute CD-RPED. This project is in collaboration with researchers in Cergy, France, where RPED experiments on Mn5Si3 are planned.Tasks
1. Compute the band structure structure of Mn5Si3 using DFT and DFT+U with the VASP code and compare with the literature
2. Examine the crystal field of the different Mn ions and build crystal field models.
3. Learn the RPED code developed by Krüger.
4. Compute the CD-RPED pattern of Mn5Si3 and analyze the data. Compare with experiment (when they become available).
[1] Libor Šmejkal, Jairo Sinova, and Tomas Jungwirth, Emerging Research Landscape of Altermagnetism, Phys. Rev. X 12, 040501 (2022).
[2] H. Reichlová et al, Observation of a spontaneous anomalous Hall response in the Mn5Si3 d-wave altermagnet candidate Nat Commun 15, 4961 (2024)
[3] P. Krüger, Circular dichroism in resonant photoelectron diffraction as a direct probe of sublattice magnetization in altermagnets. arXiv:2504.08380 (2025)
Project 4: X-ray photoelectron diffraction of TaS2
Background. Tantalum sulfide (TaS2) is a layered transition metal dichalgogenide (TDMC). Layered TDMCs are considered very promising materials for future electronic devices. TaS2 has intriguing physical properties and a rich phase diagram including a Mott-insulating state and charge-density-wave (CDW) states which may be commensurate or incommensurate depending on temperature [1]. The nature of the CDW state is the subject of on-going debate [2,3]. The aim of this project is to analyze high-resolution X-ray photoelectron diffraction (XPD) data of the TaS2 surface which has recently been acquired by Prof. F. Matsui at IMS, Japan [4]. Through the XPD analysis, the surface atomic structure will be determined with high accuracy, and this will provide important insight in the origin of the CDW state.Tasks
1. Learn XPD calculations using the EDAC [5] and/or MsSpec [6] software
2. Make a surface model of 1T-TaS2
3. Optimize the surface structure which best reproduces the experimental XPD pattern
4. Perform a DFT calculation of 1T-TaS2 with the XPD optimized structure and compare the electronic state with that reported in the literature.
[1] https://en.wikipedia.org/wiki/Tantalum(IV)_sulfide
[2] J. Lee et al., Phys. Rev. Lett. 126, 196405 (2021).
[3] M. D. Johannes and I. I. Mazin, Phys. Rev. B 77, 165135 (2008)
[4] F. Matsui, private communication
[5] http://widgets.nanophotonics.es/edac/manual/edac.html
[6] https://ipr.univ-rennes.fr/en/materials-nanosciences-department/msspec
[7] 富野陽斗,卒業研究,千葉大学, 3/2024 発表プレゼン, 用紙
Project 5: Adsorption of spin-crossover molecule Fe(phen)2(NCS)2 on O/Nb(110) surface
Background. In spin-crossover molecules, the spin state can be controlled by changing temperature, light, pressure, magnetic field or electric field. Fe(phen)2(NCS)2 is a spin-crossover molecule that is low spin below 175 K and high spin for higher temperatures. The adsorption of Fe-phen on noble metal surfaces is well studied [1-4]. However, the quite strong interaction with the metal substrate modifies the molecular structure. A weaker molecule-substrate interaction is expected for a O/Nd(110) surface [5], for with experiments are under way in Prof. T. K. Yamada's group at Chiba University. The aim of the project is to study the adsorption and magnetism of Fe-phen on O/Nd(110) through density functional theory modeling.Tasks
1. Learn surface calculations with the VASP code
2. Calculate the electronic and magnetic structure of the free Fe(phen)2(NCS)2 molecule using DFT+U.
3. Build a slab model for the O/Nd(110) surface
4. Calculate the electronic and magnetic structure of the adsorbed Fe(phen)2(NCS)2 molecule using DFT+U.
5. Simulate STM images and compare with experiment (Yamada group)
[1] M. Gruber et al., Spin crossover in Fe(phen)2(NCS)2 complexes on metallic surfaces J. Chem. Phys. 146, 092312 (2017)
[2] T. Miyamachi et al. Robust spin crossover and memristance across a single molecule Nat Commun 3, 938 (2012).
[3] Fe-phen/Ag (DFT) S. Gueddida and M. Alouani, 2014
[4] Fe-phen/Ag: XMCD-calculation R. Pasquier and M. Alouani, 2023
[5] O/Nd(110) surface, Phys. Rev. B 109, 195417 (2024)
Project 6: Atomic structure of AgPt nanowires
Background. 大川研究室Tasks
1. Learn bulk and surface calculations with the VASP code
2. Build 1-D models for nanowires of various radii and Ag:Pt composition
3. Compute the structure of these systems and find the most stable structure for given composition and diameter
4. Examine the possibility of surface segregation
[1] Cui-Ju Feng et al, First-principle study of Ag-Au double wall nanotube and nanowire, Phys. Lett. A 407, 127468 (2021)