@article{hua_structural_2025,

title = {Structural and magnetic properties of β-Li_{2}IrO_{3} after grazing-angle focused ion beam thinning},

author = {N. Hua and F. Breitner and A. Jesche and S. -W. Huang and C. Rüegg and P. Gegenwart},

url = {https://doi.org/10.1107/S2052520625000587},

doi = {10.1107/S2052520625000587},

year  = {2025},

date = {2025-04-01},

urldate = {2025-04-01},

journal = {Acta Crystallogr. B},

volume = {81},

number = {2},

pages = {202},

abstract = {Manipulating the size and orientation of quantum materials is often used to tune emergent phenomena, but precise control of these parameters is also necessary from an experimental point of view. Various synthesis techniques already exist, such as epitaxial thin film growth and chemical etching, that are capable of producing specific sample dimensions with high precision. However, certain materials exist as single crystals that are often difficult to manipulate, thereby limiting their studies to a certain subset of experimental techniques. One particular class of these materials includes lithium and sodium iridates, which are promising candidates for hosting a Kitaev quantum spin liquid state. Here a controlled method of using a focused ion beam at grazing incidence to reduce the size of a β-Li_2IrO_3 single crystal to a thickness of 1–2𝜇m is presented. Subsequent X-ray diffraction measurements show the lattice remains intact, albeit with a larger mosaic spread. The integrity of the magnetic order is also preserved as the temperature dependent magnetic diffraction peak follows the same trend as its bulk counterpart with a transition temperature at textitT = 37.5K. Our study demonstrates a technique that opens up the possibility of nonequilibrium experiments where submicron thin samples are often essential.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{wenzel_fermi-liquid_2025,

title = {Fermi-liquid behavior of nonaltermagnetic RuO_{2}},

author = {M. Wenzel and E. Uykur and S. Rößler and M. Schmidt and O. Janson and A. Tiwari and M. Dressel and A. A. Tsirlin},

url = {https://link.aps.org/doi/10.1103/PhysRevB.111.L041115},

doi = {10.1103/PhysRevB.111.L041115},

year  = {2025},

date = {2025-01-28},

urldate = {2025-01-28},

journal = {Phys. Rev. B},

volume = {111},

number = {4},

pages = {L041115},

abstract = {The presence of magnetism in potentially altermagnetic RuO2 has been a subject of intense debate. Using broadband infrared spectroscopy combined with density-functional band-structure calculations, we show that the optical conductivity of RuO2, the bulk probe of its electronic structure, is best described by a nonmagnetic model. The sharp Pauli edge demonstrates the presence of a Dirac nodal line lying 45 meV below the Fermi level. An excellent match between the experimental and ab initio plasma frequencies underpins the weakness of electronic correlations. The intraband part of the optical conductivity indicates Fermi-liquid behavior with two distinct scattering rates below 150 K. Fermi-liquid theory also accounts for the temperature-dependent magnetic susceptibility of RuO2 and allows a consistent description of this material as a paramagnetic metal.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{shen_pressure-dependent_2025,

title = {Pressure-dependent magnetism of the Kitaev candidate Li_{2}RhO_{3}},

author = {B. Shen and Insuasti Pazmino, E. and R. Dhakal and F. Freund and P. Gegenwart and S. M. Winter and A. A. Tsirlin},

url = {https://doi.org/10.1038/s41535-025-00730-1},

doi = {10.1038/s41535-025-00730-1},

year  = {2025},

date = {2025-01-22},

urldate = {2025-01-22},

journal = {npj Quantum Mater.},

volume = {10},

number = {1},

pages = {9},

abstract = {We use magnetization measurements under pressure along with ab initio and cluster many-body calculations to investigate magnetism of the Kitaev candidate Li2RhO3. Hydrostatic compression leads to a decrease in the magnitude of the nearest-neighbor ferromagnetic Kitaev coupling K1 and the corresponding increase in the off-diagonal anisotropy Γ1, whereas the experimental Curie-Weiss temperature changes from negative to positive with the slope of +40 K/GPa. On the other hand, spin freezing persists up to at least 3.46 GPa with the almost constant freezing temperature of 5 K that does not follow the large changes in the exchange couplings and indicates the likely extrinsic origin of spin freezing. Magnetic frustration in Li2RhO3 is mainly related to the interplay between ferromagnetic K1 and antiferromagnetic Γ1, along with the weakness of the third-neighbor coupling J3 that would otherwise stabilize zigzag order. The small J3 distinguishes Li2RhO3 from other Kitaev candidates.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{abdeldaim_kitaev_2024,

title = {Kitaev Interactions Through an Extended Superexchange Pathway in the j_{eff} = 1/2 Ru^{3+} Honeycomb Magnet RuP_{3}SiO_{11}},

author = {A. H. Abdeldaim and H. Gretarsson and S. J. Day and M. D. Le and G. B. G. Stenning and P. Manuel and R. S. Perry and A. A. Tsirlin and G. J. Nilsen and L. Clark},

doi = {10.1038/s41467-024-53900-3},

year  = {2024},

date = {2024-11-15},

urldate = {2024-11-15},

journal = {Nat. Commun.},

volume = {15},

number = {1},

pages = {9778},

abstract = {Magnetic materials are composed of the simple building blocks of magnetic moments on a crystal lattice that interact via magnetic exchange. Yet from this simplicity emerges a remarkable diversity of magnetic states. Some reveal the deep quantum mechanical origins of magnetism, for example, quantum spin liquid (QSL) states in which magnetic moments remain disordered at low temperatures despite being strongly correlated through quantum entanglement. A promising theoretical model of a QSL is the Kitaev model, composed of unusual bond-dependent exchange interactions, but experimentally, this model is challenging to realise. Here we show that the material requirements for the Kitaev QSL survive an extended pseudo-edge-sharing superexchange pathway of Ru3+ octahedra within the honeycomb layers of the inorganic framework solid, RuP3SiO11. We confirm the requisite 

 state of Ru3+ in RuP3SiO11 and resolve the hierarchy of exchange interactions that provide experimental access to an unexplored region of the Kitaev model.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{shen_strong_2024,

title = {Strong Enhancement of Magnetic Coercivity Induced by Uniaxial Stress},

author = {B. Shen and F. Breitner and P. Gegenwart and A. Jesche},

doi = {10.1103/PhysRevLett.133.186702},

year  = {2024},

date = {2024-10-28},

urldate = {2024-10-28},

journal = {Phys. Rev. Lett.},

volume = {133},

number = {18},

pages = {186702},

abstract = {The performance of permanent magnets is intricately tied to their magnetic hysteresis loop. In this study, we investigate the heavy-fermion ferromagnet CeAgSb2 through magnetization measurements under uniaxial stress. We observe a 2400% increase in magnetic coercivity with just a modest stress of approximately 1 kbar. This effect persists even after pressure release, attributable to stress-induced defects that efficiently pin domain walls. Other magnetic properties such as ordering temperature and saturation moment exhibit only weak pressure dependencies and display full reversibility. Our findings offer a promising route for increasing coercive field strength and enhancing the energy product in ferromagnetic materials and are potentially applicable to a broad spectrum of commercial or emerging magnetic applications.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{mukharjee_intermediate_2024,

title = {Intermediate field-induced phase of the honeycomb magnet BaCo_{2}(AsO_{4})_{2}},

author = {P. K. Mukharjee and B. Shen and S. Erdmann and A. Jesche and J. Kaiser and P. R. Baral and O. Zaharko and P. Gegenwart and A. A. Tsirlin},

doi = {10.1103/PhysRevB.110.L140407},

year  = {2024},

date = {2024-10-21},

urldate = {2024-10-21},

journal = {Phys. Rev. B},

volume = {110},

number = {14},

pages = {L140407},

abstract = {We use magnetometry, calorimetry, and high-resolution capacitive dilatometry, as well as single-crystal neutron diffraction to explore the temperature-field phase diagram of the anisotropic honeycomb magnet BaCo2⁢(AsO4)2. Our data reveal four distinct ordered states observed for in-plane magnetic fields. Of particular interest is the narrow region between 0.51 and 0.54 T that separates the up-up-down order from the fully polarized state and coincides with the field range where signatures of the spin-liquid behavior have been reported. We show that magnetic Bragg peaks persist in this intermediate phase, thus ruling out its spin-liquid nature. However, the simultaneous nonmonotonic evolution of nuclear Bragg peaks suggests the involvement of the lattice, witnessed also in other regions of the phase diagram where large changes in the sample length are observed upon entering the magnetically ordered states. Our data highlight the importance of lattice effects in BaCo2⁢(AsO4)2.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{reinhoffer_strong_2024,

title = {Strong Terahertz Third-Harmonic Generation by Kinetic Heavy Quasiparticles in CaRuO_{3}},

author = {C. Reinhoffer and S. Esser and S. Esser and E. Mashkovich and S. Germanskiy and P. Gegenwart and F. Anders and P. H. M. Loosdrecht and Z. Wang},

url = {https://link.aps.org/doi/10.1103/PhysRevLett.132.196501},

doi = {10.1103/PhysRevLett.132.196501},

year  = {2024},

date = {2024-05-08},

urldate = {2024-05-08},

journal = {Phys. Rev. Lett.},

volume = {132},

number = {19},

pages = {196501},

abstract = {We report on time-resolved nonlinear terahertz spectroscopy of a strongly correlated ruthenate, CaRuO_{3}, as a function of temperature, frequency, and terahertz field strength. Third-harmonic radiation for frequencies up to 2.1 THz is observed evidently at low temperatures below 80 K, where the low-frequency linear dynamical response deviates from the Drude model and a coherent heavy quasiparticle band emerges by strong correlations associated with the Hund’s coupling. Phenomenologically, by taking an experimentally observed frequency-dependent scattering rate, the deviation of the field driven kinetics from the Drude behavior is reconciled in a time-dependent Boltzmann description, which allows an attribution of the observed third-harmonic generation to the terahertz field driven nonlinear kinetics of the heavy quasiparticles.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{solana-madruga_covo_3_2023,

title = {CoVO_{3} High-Pressure Polymorphs: To Order or Not to Order?},

author = {E. Solana-Madruga and O. Mentre and A. A. Tsirlin and M. Huve and D. Khalyavin and C. Ritter and A. M. Arevalo-Lopez},

doi = {10.1002/advs.202307766},

year  = {2024},

date = {2024-03-06},

urldate = {2023-12-01},

journal = {Adv. Sci.},

volume = {11},

number = {9},

pages = {2307766},

abstract = {Materials properties are determined by their compositions and structures. In ABO(3) oxides different cation orderings lead to mainly perovskite- or corundum like derivatives with exciting physical properties. Sometimes, a material can be stabilized in more than one structural modification, providing a unique opportunity to explore structure-properties relationship. Here, CoVO3 obtained in both ilmenite-(CoVO3-I) and LiNbO3-type (CoVO3-II) polymorphs at moderate (8-12 GPa) and high pressures (22 GPa), respectively are presented. Their distinctive cation distributions affect drastically the magnetic properties as CoVO3-II shows a cluster-glass behavior while CoVO3-I hosts a honeycomb zigzag magnetic structure in the cobalt network. First principles calculations show that the influence of vanadium is crucial for CoVO3-I, although it is previously considered as non-magnetic in a dimerized spin-singlet state. Contrarily, CoVO3-II shows two independent interpenetrating antiferromagnetic Co- and ferromagnetic V-hcp sublattices, which intrinsically frustrate any possible magnetic order. CoVO3-II is also remarkable as the first oxide crystallizing with the LiNbO3-type structure where both metals contain free d electrons. CoVO3 polymorphs pinpoint therefore as well to a much broader phase field of high-pressure A-site Cobaltites.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{shen_magnetic_2024,

title = {Magnetic vs. nonmagnetic polymorphs of RuBr_{3} under pressure},

author = {B. Shen and V. A. Ginga and A. M. Arévalo-López and G. Garbarino and E. Uykur and M. Goncalves-Faria and P. K. Mukharjee and P. Gegenwart and A. A. Tsirlin},

doi = {10.1103/PhysRevB.109.224402},

year  = {2024},

date = {2024-03-01},

urldate = {2024-03-01},

journal = {Phys. Rev. B},

volume = {109},

number = {22},

pages = {224402},

abstract = {Pressure evolution of the crystal structure and magnetism of the honeycomb 𝛼-RuBr_3 is studied using high-pressure x-ray diffraction, magnetometry, and density-functional band-structure calculations. Hydrostatic compression transforms antiferromagnetic 𝛼-RuBr_3 (R-3) into paramagnetic 𝛼'-RuBr_3 (P-1) where short Ru-Ru bonds cause magnetism collapse above 1.3 GPa at 0 K and 2.5 GPa at 295 K. Below this critical pressure, the Ntextbackslash'eel temperature of 𝛼-RuBr_3 increases with the slope of 1.8 K/GPa. Pressure tunes 𝛼-RuBr_3 away from the Kitaev limit, whereas increased third-neighbor in-plane coupling and interlayer coupling lead to a further stabilization of the collinear zigzag state. Both 𝛼- and 𝛼'-RuBr_3 are metastable at ambient pressure, but their transformation into the thermodynamically stable 𝛽-polymorph is kinetically hindered at room temperature.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{panther_frustration_2023,

title = {Frustration relief and reorientation transition in the kagomelike dolerophanite Cu_{2}OSO_{4}},

author = {A. Panther and A. A. Tsirlin and I. Rousochatzakis},

doi = {10.1103/PhysRevB.108.224410},

year  = {2023},

date = {2023-12-01},

urldate = {2023-12-01},

journal = {Phys. Rev. B},

volume = {108},

number = {22},

pages = {224410},

abstract = {We present a theoretical study of dolerophanite Cu2OSO4, a layered kagomelike spin-21 magnetic insulator that can be described either as a system of chains coupled through dimers or as a kagome lattice where every third spin is replaced by a ferromagnetic spin dimer. Building on insights from ab initio calculations, classical numerical minimizations, and semiclassical expansions, we arrive at a minimal microscopic description that accounts for the experimental data reported so far, including the nature of the magnetic order, the reported spin length, and the observed anisotropy. The latter arises by a peculiar competition between the antisymmetric (DzyaloshinskiiMoriya) and the symmetric part of the exchange anisotropy, which gives rise to a two-step reorientation process involving two successive continuous phase transitions. In this paper, we uncover mechanisms stabilizing canted ferrimagnetic order in kagome systems and highlight strong magnetic anisotropy in the presence of dissimilar magnetic orbitals on crystallographically nonequivalent Cu sites. We also show how these anisotropy terms affect the spin-wave spectrum and how they can be tracked experimentally.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{breitner_metallic_2023,

title = {Metallic conductivity in Na-deficient structural domain walls in the spin-orbit Mott insulator Na_{2}IrO_{3}},

author = {F. A. Breitner and J. Kaiser and A. Jesche and P. Gegenwart},

doi = {10.1103/PhysRevB.108.235130},

year  = {2023},

date = {2023-12-01},

urldate = {2023-12-01},

journal = {Phys. Rev. B},

volume = {108},

number = {23},

pages = {235130},

abstract = {Honeycomb Na2IrO3 is a prototype spin-orbit Mott insulator and Kitaev magnet. We report a combined structural and electrical resistivity study of Na2IrO3 single crystals. Laue back-scattering diffraction indicates twinning with +/- 120 degrees rotation around the c* axis while scanning electron microscopy displays nanothin lines parallel to all three b-axis orientations of twin domains. Energy dispersive x-ray analysis line scans across such domain walls indicate no change of the Ir signal intensity, i.e., intact honeycomb layers, while the Na intensity is reduced down to similar to 2/3 of its original value at the domain walls, implying significant hole doping. Utilizing focused-ion-beam microsectioning, the temperature dependence of the electrical resistance of individual domain walls is studied. It demonstrates the tuning through the metal-insulator transition into a correlated-metal ground state by increasing hole doping.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}