insight - Scientific Computing - # Altermagnetism

The Fragility of Altermagnetism in LaTiO3: How Orbital Disorder Suppresses Spin Splitting

Q: Could external factors like strain or pressure be used to influence orbital ordering and thus altermagnetism in LaTiO3?

Yes, external factors like strain and pressure hold significant potential to influence orbital ordering and, consequently, altermagnetism in LaTiO3. Here's how these factors come into play: Strain: As mentioned earlier, strain can distort the crystal lattice, directly impacting the delicate energy balance between the t2g orbitals. Applying uniaxial or biaxial strain can either reinforce or disrupt the specific orbital arrangement needed for altermagnetism. For example, if strain increases the energy of the (l = 2, m = -2) orbital relative to the (l = 2, m = ±1) orbitals, it would promote the single-orbital occupancy conducive to altermagnetism. Conversely, strain that equalizes the energies of these orbitals would likely lead to multi-orbital filling and suppress altermagnetism. Pressure: Applying hydrostatic pressure compresses the entire crystal lattice, modifying the overlap between atomic orbitals. This pressure-induced change in orbital overlap can shift the relative energies of the t2g orbitals, potentially favoring or hindering the specific orbital filling required for altermagnetism. The sensitivity of LaTiO3's electronic structure to pressure, as evidenced by its pressure-induced metal-insulator transition, suggests that pressure could be a viable tuning parameter for its magnetic properties as well. Essentially, both strain and pressure provide mechanisms to manipulate the delicate energy balance that governs orbital ordering in LaTiO3. By carefully tuning these external stimuli, one could potentially drive transitions between altermagnetic and conventional antiferromagnetic states, highlighting their potential for controlling the material's magnetic properties.

Q: If altermagnetism is fundamentally a result of specific orbital arrangements, could similar phenomena be observed in systems beyond traditional electronic materials, such as in cold atom systems or photonic lattices?

The intriguing possibility of observing altermagnetism-like phenomena in systems beyond traditional electronic materials, such as cold atom systems or photonic lattices, hinges on replicating the key ingredients that give rise to altermagnetism. While challenging, it's not entirely implausible. Here's a breakdown of the considerations: Cold Atom Systems: Ultracold atoms trapped in optical lattices offer a remarkable platform to simulate condensed matter phenomena. To mimic altermagnetism, one would need to engineer artificial gauge fields that mimic the effects of spin-orbit coupling and potentially break time-reversal symmetry in a controlled manner. Achieving the specific orbital-like arrangements within the lattice, along with the necessary symmetry breaking, would be crucial. While experimentally demanding, the remarkable tunability of cold atom systems makes them an exciting testbed for exploring such exotic magnetic states. Photonic Lattices: Photonic lattices, where light is confined within a periodic structure, provide another avenue. The challenge lies in replicating the spin-dependent interactions and orbital-like degrees of freedom found in electronic systems. Recent advances in topological photonics and the creation of synthetic gauge fields for photons offer promising pathways. For instance, by carefully designing the geometry and topology of photonic lattices, one might be able to mimic the orbital physics and symmetry breaking necessary for altermagnetism-like behavior. The key takeaway is that while observing altermagnetism in these systems presents significant hurdles, it's not beyond the realm of possibility. The rapid advancements in manipulating and controlling cold atoms and photons provide a glimmer of hope for realizing and studying such exotic magnetic states in these unconventional platforms.

Core Concepts

While LaTiO3 exhibits altermagnetism due to its specific crystal symmetry and single-electron orbital filling, this property is fragile and can be suppressed by orbital disorder, leading to a conventional antiferromagnetic state.

Abstract

Bibliographic Information: Maznichenko, I. V., Ernst, A., Maryenko, D., Dugaev, V. K., Sherman, E. Y., Buczek, P., Parkin, S. S. P., & Ostanin, S. (2024). Fragile altermagnetism and orbital disorder in Mott insulator LaTiO3. arXiv preprint arXiv:2411.00583v1.
Research Objective: This study investigates the presence of altermagnetism in LaTiO3 and the impact of orbital disorder on its electronic and magnetic properties.
Methodology: The researchers employed first-principles calculations using the Korringa-Kohn-Rostoker (KKR) Green's function method within the density functional theory (DFT) framework. They simulated orbital disorder using the coherent potential approximation (CPA).
Key Findings:
- LaTiO3 exhibits an altermagnetic ground state characterized by fully compensated antiferromagnetism and k-dependent spin-split electron bands in the absence of spin-orbit coupling.
- This altermagnetism is driven by the specific arrangement of Ti d-orbitals with a single electron occupying the (l=2, m= -1, sz= +1/2) and (l=2, m= +1, sz= -1/2) states in each unit cell.
- Introducing orbital disorder by distributing the electron charge among multiple t2g orbitals weakens and eventually eliminates the spin splitting, leading to a transition from an altermagnetic to a conventional antiferromagnetic state.
Main Conclusions:
- The altermagnetic state in LaTiO3 is fragile and highly sensitive to orbital disorder.
- Orbital fluctuations, potentially induced by factors like spin-orbit coupling, can disrupt the specific orbital filling required for altermagnetism.
Significance:
- This study provides valuable insights into the factors influencing altermagnetism in materials.
- It highlights the importance of orbital ordering in realizing and controlling altermagnetic properties.
Limitations and Future Research:
- The study doesn't explicitly consider the effects of spin-orbit coupling, which could further influence orbital disorder and altermagnetism.
- Further experimental investigations are crucial to confirm the theoretical predictions and explore the potential applications of altermagnetic LaTiO3.

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Stats

The band gap in LaTiO3 is 0.22 eV.
Each Ti3+ ion in LaTiO3 has a magnetic moment of ~0.8µB.
The DFT+U calculations used correlation parameters Ueff of 2.3 eV for Ti 3d states and 6 eV for La f states.

Quotes

"The altermagnetic ground state of LTO is protected by the crystal symmetry and specifically ordered d-orbitals of Ti ions."
"When at least two d orbitals of Ti become almost equally filled, altermagnetic LTO transforms into an antiferromagnet."

Key Insights Distilled From

Fragile altermagnetism and orbital disorder in Mott insulator LaTiO$_3$

by I. V. Maznic... at arxiv.org 11-04-2024

https://arxiv.org/pdf/2411.00583.pdf

Fragile altermagnetism and orbital disorder in Mott insulator LaTiO$_3$

Deeper Inquiries

How could the manipulation of orbital occupancy be used to control the electronic and magnetic properties of LaTiO3 and other potential altermagnets?

Manipulating orbital occupancy in LaTiO3 and other potential altermagnets presents a compelling route to fine-tune their electronic and magnetic properties. The article highlights the delicate balance of orbital filling in dictating whether LaTiO3 exhibits altermagnetism or conventional antiferromagnetism.
Here's how orbital occupancy manipulation can be leveraged:

Strain Engineering: Applying strain can distort the crystal lattice, directly influencing the energy levels and filling of the t2g orbitals in LaTiO3. By inducing compressive or tensile strain, one could potentially drive the system between an altermagnetic state (favored by specific single-orbital occupancy) and an antiferromagnetic state (resulting from multi-orbital contributions). This control stems from the strain modifying the overlap between atomic orbitals, thereby shifting their relative energies.

Chemical Doping/Substitution: Introducing dopants into the LaTiO3 lattice can alter the electron count and influence orbital occupancy. For instance, substituting La3+ with a divalent cation would introduce holes, potentially driving the system towards a multi-orbital filling scenario and suppressing altermagnetism. Conversely, electron doping could be achieved by substituting Ti3+ with a tetravalent cation. This method provides a chemical pathway to tip the balance between different magnetic ground states.

Electric Fields: Applying an external electric field can shift the energy levels of orbitals with different spatial orientations. In the context of LaTiO3, a carefully oriented electric field could be used to selectively manipulate the filling of the t2g orbitals, potentially favoring the specific orbital arrangement required for altermagnetism. This approach offers a dynamic way to control orbital occupancy and, consequently, the magnetic state.
The key takeaway is that by precisely controlling which t2g orbitals are preferentially occupied, we can effectively toggle the magnetic behavior of LaTiO3 and similar altermagnets. This control over orbital filling opens doors to engineering materials with switchable magnetic properties, potentially enabling novel spintronic devices.

Could external factors like strain or pressure be used to influence orbital ordering and thus altermagnetism in LaTiO3?

Yes, external factors like strain and pressure hold significant potential to influence orbital ordering and, consequently, altermagnetism in LaTiO3.
Here's how these factors come into play:

Strain: As mentioned earlier, strain can distort the crystal lattice, directly impacting the delicate energy balance between the t2g orbitals. Applying uniaxial or biaxial strain can either reinforce or disrupt the specific orbital arrangement needed for altermagnetism. For example, if strain increases the energy of the (l = 2, m = -2) orbital relative to the (l = 2, m = ±1) orbitals, it would promote the single-orbital occupancy conducive to altermagnetism. Conversely, strain that equalizes the energies of these orbitals would likely lead to multi-orbital filling and suppress altermagnetism.

Pressure: Applying hydrostatic pressure compresses the entire crystal lattice, modifying the overlap between atomic orbitals. This pressure-induced change in orbital overlap can shift the relative energies of the t2g orbitals, potentially favoring or hindering the specific orbital filling required for altermagnetism. The sensitivity of LaTiO3's electronic structure to pressure, as evidenced by its pressure-induced metal-insulator transition, suggests that pressure could be a viable tuning parameter for its magnetic properties as well.
Essentially, both strain and pressure provide mechanisms to manipulate the delicate energy balance that governs orbital ordering in LaTiO3. By carefully tuning these external stimuli, one could potentially drive transitions between altermagnetic and conventional antiferromagnetic states, highlighting their potential for controlling the material's magnetic properties.

If altermagnetism is fundamentally a result of specific orbital arrangements, could similar phenomena be observed in systems beyond traditional electronic materials, such as in cold atom systems or photonic lattices?

The intriguing possibility of observing altermagnetism-like phenomena in systems beyond traditional electronic materials, such as cold atom systems or photonic lattices, hinges on replicating the key ingredients that give rise to altermagnetism. While challenging, it's not entirely implausible.
Here's a breakdown of the considerations:

Cold Atom Systems: Ultracold atoms trapped in optical lattices offer a remarkable platform to simulate condensed matter phenomena. To mimic altermagnetism, one would need to engineer artificial gauge fields that mimic the effects of spin-orbit coupling and potentially break time-reversal symmetry in a controlled manner. Achieving the specific orbital-like arrangements within the lattice, along with the necessary symmetry breaking, would be crucial. While experimentally demanding, the remarkable tunability of cold atom systems makes them an exciting testbed for exploring such exotic magnetic states.

Photonic Lattices: Photonic lattices, where light is confined within a periodic structure, provide another avenue. The challenge lies in replicating the spin-dependent interactions and orbital-like degrees of freedom found in electronic systems. Recent advances in topological photonics and the creation of synthetic gauge fields for photons offer promising pathways. For instance, by carefully designing the geometry and topology of photonic lattices, one might be able to mimic the orbital physics and symmetry breaking necessary for altermagnetism-like behavior.
The key takeaway is that while observing altermagnetism in these systems presents significant hurdles, it's not beyond the realm of possibility. The rapid advancements in manipulating and controlling cold atoms and photons provide a glimmer of hope for realizing and studying such exotic magnetic states in these unconventional platforms.