CM Seminar : Dimensional reduction by geometrical frustration

Event Date:
2020-03-10T14:00:00
2020-03-10T15:00:00
Event Location:
Brimacombe 311
Speaker:
Zenji Hiroi
Related Upcoming Events:
Condensed Matter Seminars
Intended Audience:
Public
Event Information:

Dimensionality is one of the most important factors that critically govern phase transitions and elementary excitations in solids. Low dimensional spin systems are approximately materialized in actual three-dimensional (3D) crystals via anisotropic chemical bonding. However, dimensionality may not be always a “built-in” character of a crystal structure but can be an emergent property in a frustrated spin system. One example is found in BaCu2Si2O6, in which BEC of triplons takes an essentially 2D character near a quantum critical point between the gapped state and long-range order [1]. This is ascribed to a geometrical frustration between neighboring square lattices that stack in a staggered manner so as to cancel the inter-layer couplings. Thus, true two-dimensionality seems to be preserved by frustration in the 3D lattice.

Here we report “dimensional reduction” by geometrical frustration in three spin systems. In Ca3ReO5Cl2 comprising an anisotropic triangular lattice (ATL) made of spin-1/2 Re6+ ions, one dimensionalization is clearly evidenced by magnetic susceptibility and heat capacity measurements, in spite that the inter-chain zigzag coupling is significantly large: J’/J = 0.42 [2]. A similar one dimensionalization gives a singlet ground state in the two-leg spin ladder compound SrCu2O3 and a 1D spin liquid in the three-leg spin ladder compound Sr2Cu3O5 [3].

Figure 1: Magnetic order in pharmacosiderite

Further interesting dimensional reduction is recently observed in a natural mineral, pharmocosiderite (H3O)Fe4(AsO4)3(OH)4•5.5H2O [4]. It comprises tetrahedral clusters made of spin-5/2 Fe3+ ions in a cubic primitive cell (Fig. 1). The antiferromagnetic Heisenberg interactions are determined as J = 10.6 K and J’ = 2.9 K. A q = 0, Γ5 order sets in at 6 K, in which a 2D spin fluctuation is observed. This is ascribed to a two dimensionalization by frustration only for the J’ tetrahedral coupling along the c axis. It is emphasized that, compared with the ATL antiferromagnets, the resulting 2D anisotropy is not fixed to the crystal lattice but is induced by the evolution of magnetic correlations towards the LRO.

 

 

[1] S. E. Sebastian, et al., Nature 441, 617 (2006).

[2] D. Hirai , et al., J. Phys. Soc. Jpn. 88 044708 (2019).

[3] M. Azuma, et al., Phys. Rev. Lett. 73, 3463 (1994).

[4] R. Okuma, et al., J. Phys. Soc. Jpn. 87, 093702 (2018).

Add to Calendar 2020-03-10T14:00:00 2020-03-10T15:00:00 CM Seminar : Dimensional reduction by geometrical frustration Event Information: Dimensionality is one of the most important factors that critically govern phase transitions and elementary excitations in solids. Low dimensional spin systems are approximately materialized in actual three-dimensional (3D) crystals via anisotropic chemical bonding. However, dimensionality may not be always a “built-in” character of a crystal structure but can be an emergent property in a frustrated spin system. One example is found in BaCu2Si2O6, in which BEC of triplons takes an essentially 2D character near a quantum critical point between the gapped state and long-range order [1]. This is ascribed to a geometrical frustration between neighboring square lattices that stack in a staggered manner so as to cancel the inter-layer couplings. Thus, true two-dimensionality seems to be preserved by frustration in the 3D lattice. Here we report “dimensional reduction” by geometrical frustration in three spin systems. In Ca3ReO5Cl2 comprising an anisotropic triangular lattice (ATL) made of spin-1/2 Re6+ ions, one dimensionalization is clearly evidenced by magnetic susceptibility and heat capacity measurements, in spite that the inter-chain zigzag coupling is significantly large: J’/J = 0.42 [2]. A similar one dimensionalization gives a singlet ground state in the two-leg spin ladder compound SrCu2O3 and a 1D spin liquid in the three-leg spin ladder compound Sr2Cu3O5 [3]. Figure 1: Magnetic order in pharmacosiderite Further interesting dimensional reduction is recently observed in a natural mineral, pharmocosiderite (H3O)Fe4(AsO4)3(OH)4•5.5H2O [4]. It comprises tetrahedral clusters made of spin-5/2 Fe3+ ions in a cubic primitive cell (Fig. 1). The antiferromagnetic Heisenberg interactions are determined as J = 10.6 K and J’ = 2.9 K. A q = 0, Γ5 order sets in at 6 K, in which a 2D spin fluctuation is observed. This is ascribed to a two dimensionalization by frustration only for the J’ tetrahedral coupling along the c axis. It is emphasized that, compared with the ATL antiferromagnets, the resulting 2D anisotropy is not fixed to the crystal lattice but is induced by the evolution of magnetic correlations towards the LRO.     [1] S. E. Sebastian, et al., Nature 441, 617 (2006). [2] D. Hirai , et al., J. Phys. Soc. Jpn. 88 044708 (2019). [3] M. Azuma, et al., Phys. Rev. Lett. 73, 3463 (1994). [4] R. Okuma, et al., J. Phys. Soc. Jpn. 87, 093702 (2018). Event Location: Brimacombe 311