Significant softening ofc66and hidden order parameter in the magnetic ordered state ofLa2−xCaxCoO4(0.4≤x≤0.7)

Order parameter of non-magnetic phase transition at 105 K, which is called "hidden order", was revealed in spin-orbit coupled iridate Ca5Ir3O12. This discover of order parameter with rotational and directional degrees of freedom in atomic scale will lead to development of energy saving devices with a fast cross-correlated response.

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From hidden order to antiferromagnetism: Electronic structure changes in Fe-doped URu2Si2

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2020750118 ◽

2021 ◽

Vol 118 (27) ◽

pp. e2020750118

Author(s):

Emmanouil Frantzeskakis ◽

Ji Dai ◽

Cédric Bareille ◽

Tobias C. Rödel ◽

Monika Güttler ◽

...

Keyword(s):

Phase Transition ◽

Electronic Structure ◽

Fermi Level ◽

Order Parameter ◽

Heavy Fermion ◽

Interaction Strength ◽

Magnetization Vector ◽

Angle Resolved Photoemission Spectroscopy ◽

Hidden Order ◽

Structure Changes

In matter, any spontaneous symmetry breaking induces a phase transition characterized by an order parameter, such as the magnetization vector in ferromagnets, or a macroscopic many-electron wave function in superconductors. Phase transitions with unknown order parameter are rare but extremely appealing, as they may lead to novel physics. An emblematic and still unsolved example is the transition of the heavy fermion compound URu2Si2 (URS) into the so-called hidden-order (HO) phase when the temperature drops below T0=17.5 K. Here, we show that the interaction between the heavy fermion and the conduction band states near the Fermi level has a key role in the emergence of the HO phase. Using angle-resolved photoemission spectroscopy, we find that while the Fermi surfaces of the HO and of a neighboring antiferromagnetic (AFM) phase of well-defined order parameter have the same topography, they differ in the size of some, but not all, of their electron pockets. Such a nonrigid change of the electronic structure indicates that a change in the interaction strength between states near the Fermi level is a crucial ingredient for the HO to AFM phase transition.

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Direct bulk-sensitive probe of 5fsymmetry in URu2Si2

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1612791113 ◽

2016 ◽

Vol 113 (49) ◽

pp. 13989-13994 ◽

Cited By ~ 16

Author(s):

Martin Sundermann ◽

Maurits W. Haverkort ◽

Stefano Agrestini ◽

Ali Al-Zein ◽

Marco Moretti Sala ◽

...

Keyword(s):

Ground State ◽

Order Parameter ◽

Spectroscopic Technique ◽

Quantum States ◽

Scattering Function ◽

X Ray ◽

X Ray Scattering ◽

Hidden Order ◽

Singlet States ◽

Second Order Phase Transition

The second-order phase transition into a hidden order phase in URu2Si2goes along with an order parameter that is still a mystery, despite 30 years of research. However, it is understood that the symmetry of the order parameter must be related to the symmetry of the low-lying local electronicf-states. Here, we present results of a spectroscopic technique, namely core-level nonresonant inelastic X-ray scattering (NIXS). This method allows for the measurement of local high-multipole excitations and is bulk-sensitive. The observed anisotropy of the scattering function unambiguously shows that the 5fground-state wave function is composed mainly of theΓ1with majorityJz=|4⟩+|−4⟩and/orΓ2singlet states. The incomplete dichroism indicates the possibility that quantum states of other irreducible representation are mixed into the ground state.

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Двумерные O(n)-модели с дефектами типа "случайная локальная анизотропия"

Физика твердого тела ◽

10.21883/ftt.2020.04.49128.650 ◽

2020 ◽

Vol 62 (4) ◽

pp. 610

Author(s):

А.А. Берзин ◽

А.И. Морозов ◽

А.С. Сигов

Keyword(s):

Phase Transition ◽

Phase Diagram ◽

Order Parameter ◽

Easy Axis ◽

Critical Value ◽

Smooth Transition ◽

Two Dimensional ◽

Continuous Symmetry ◽

Local Anisotropy ◽

Ordered State

The phase diagram of two-dimensional systems with continuous symmetry of the vector order parameter containing defects of the “random local anisotropy” type is investigated. In the case of a weakly anisotropic distribution of the easy anisotropy axes in the space of the order parameter, with decreasing temperature, a smooth transition takes place from the paramagnetic phase with dynamic fluctuations of the order parameter to the Imri-Ma phase with its static fluctuations. In the case when the anisotropic distribution of the easy axes induces a global anisotropy of the “easy axis” type that exceeds a critical value, the system goes into the Ising class of universality, and a phase transition to the ordered state occurs in it at a finite temperature.

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Дальний порядок в двумерных O(n)-моделях, индуцированный случайными полями, и состояние Имри-Ма

Физика твердого тела ◽

10.21883/ftt.2020.02.48880.575 ◽

2020 ◽

Vol 62 (2) ◽

pp. 281

Author(s):

А.А. Берзин ◽

А.И. Морозов ◽

А.С. Сигов

Keyword(s):

Phase Transition ◽

Local Field ◽

Random Fields ◽

Order Parameter ◽

Smooth Transition ◽

Two Dimensional ◽

Strong Anisotropy ◽

Continuous Symmetry ◽

Weak Anisotropy ◽

Ordered State

A.A. Berzin, A.I. Morosov, and A.S. Sigov The influence of defects of the “random local field” type with an anisotropic distribution of random fields on two-dimensional models with continuous symmetry of the vector order parameter is considered. In the case of weak anisotropy of random fields, with decreasing temperature there takes place a smooth transition from the paramagnetic phase with dynamic fluctuations of the order parameter to the Imry-Ma phase with static fluctuations caused by fluctuations of the random field of defects. In the case of strong anisotropy of random fields, defects lead to an effective decrease in the number of components of the order parameter and the appearance of a phase transition to an ordered state at finite temperature.

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