Jacob Linder

Jacob Linder is a professor at the Department of physics at NTNU. He has a PhD in theoretical physics obtained in 2009 and has previously worked as a postdoctoral researcher and an associate professor. He is specializing in quantum condensed matter theory.

Jacob is from Stockholm, Sweden and came to NTNU in 2000 as a fresh student at the siv.ing.-programme of physics and mathematics.

Employee profile with contact information

Multitasking: a highway to self-deception
  18 February, 2016


Asserting to ourselves that we work efficiently is something we strive for – it’s hard to beat the feeling of having been really productive after a long day at work. To accomplish this, it seems incredibly inefficient to just do one thing at a time while you’re working, doesn’t it. Why should you, when you can check your email or social media, eat your lunch, while writing a report and planning the important meeting you have tomorrow all at once.

Let’s pause for a second. How certain are you that juggling all kinds of activities throughout the day is the most efficient way to work?

It does seem impressive. Getting a lot of stuff done, more or less at the same time, has to be a remarkable feat. However, the research you’re about to get acquainted with might prompt you to reconsider.

Multitaskers worse at multitasking

Researchers at Stanford [1] and Ohio [2] university published a few years ago studies where they, among other things, compared the following two groups:

  1. Persons who multitasked heavily and who believed that doing so made them more efficient than others
  2. Persons who preferred to focus on one task at a time

As you might suspect by now, the second group accomplished to get more work done. But here’s the kicker: the researchers found that the persons in the first group, the self-confessed multitaskers, were actually worse at multitasking than those in group two! That’s gotta hurt.

It turns out our brains aren’t really built for multitasking. In fact, they are pretty terrible at it. The studies in [1] and [2] found that we become less productive and work more slowly when multitasking.


So why do we do it? The reason is that it makes us feel great: we think we’re being super efficient while in reality we’d be much better off focusing on one thing at a time.

Of course, there are plenty of activities outside of work that leaves us little choice but to multitask if we want to be successful. If you’re a professional e-gamer competing in real-time strategy games such as Starcraft or League of Legends or a chef preparing a complex dish for a dinner party of ten, you will never excel unless you can multitask like a hero.

But when it comes to doing scientific research or teaching, the studies in [1] and [2] suggest that there is little reason to multitask and that you are tricking yourself into thinking you are more efficient than what is really the case. I encourage you to have a look at these studies – they certainly made me repent and change my multitasking ways.

[1] E. Ophira, C. Nass, and A. D. Wagner. Cognitive control in media multitaskers. PNAS 106, 15583 (2009)

[2] Z. Wang and J. M. Tchernev. The “Myth” of Media Multitasking: Reciprocal Dynamics of Media Multitasking, Personal Needs, and Gratifications.
Journal of Communication 62, 493–513 (2012)


Superconducting spintronics
  9 April, 2015

New and enhanced effects in spintronics emerge when using superconducting materials. The right combination of materials that merge superconductivity and spintronics creates, for instance, a flow of spins that has zero resistance. This could eventually lead to new types of functionality in low-temperature technology.

Whereas electronics is the foundation for modern technology, the field of spintronics (or spin-dependent electronics) has in the recent decades proven to hold a real potential for generating technological advancements that may not only complement, but even replace conventional semiconductor-transistor based devices. The giant magnetoresistance effect is one of the most well-known direct implementation of spintronics in everyday appliances, in this particular case pertaining to harddrive technology and magnetic random access memory.

Illustration of two different ways to use superconducting spintronics

Superconductivity and magnetic order
The general objective of spintronics is to find ways to generate, manipulate, and detect spin flow. At first glance, spintronics might seem completely incompatible with superconducting order since superconductors in general expel magnetic fields and are comprised of spinless Cooper pairs as the fundamental building block.

Remarkably, it turns out that superconductivity can adapt to the presence of magnetic order by creating an unusual type of spin-polarized superconductivity. This type of pairing is robust not only toward impurity scattering, but also toward the paramagnetic limitation of a magnetic field.

As shown by the illustration above: When a superconductor is placed in proximity to a magnetic material, superconducting correlations will leak into the ferromagnet due to quantum mechanical tunneling. These correlations typically decay very quickly inside the ferromagnet. However, when there exists a magnetic inhomogeneity such as a domain wall near the interface, a new type of spin-polarized superconductivity emerges which can survive in the ferromagnet over very large distances.

Merging superconductivity and spintronics
Now, traditional studies that combine spintronics and superconductivity have mainly investigated injection of spin-polarized quasiparticles into superconductors. However, a synergy between superconducting and magnetic material turns out to be possible through the creation of spin-polarized superconductivity, as described above. This type of superconductivity can arise at carefully engineered superconductor interfaces with ferromagnetic materials.

There is presently intense activity focused on identifying materials combinations that merge superconductivity and spintronics to enhance device performance or even create new types of functionality. The results look very promising. It has been shown, for example, that superconducting order can strongly improve central effects in spintronics such as magnetoresistance and spin injection.

Illustration of different ways to use superconducting spintronics

New possibilities
The intersection between superconductivity and magnetism represents an exciting research arena. On the one hand, it hosts very rich fundamental quantum physics – on the other hand, it also holds the potential for creating novel types of quantum-based technology in low temperature nanoelectronics.

The illustration a) shows a schematic overview of different ways to use superconducting spintronics, both in equilibrium and non-equilibrium. Different types of common experimental setups are depicted in b)-d).

In a recent publication in Nature Physics, me and my colleague Jason W. Robinson (Cambridge University) discuss how spintronics effects can be improved when using superconducting materials:
Superconducting spintronics. J. Linder & J. W. A. Robinson, Nature Physics 11, 307–315 (2015) doi:10.1038/nphys3242.


How to choose a research area?
  13 February, 2015

Being a scientific researcher gives you the freedom to pursue answers to questions that you, and hopefully many others, find interesting. But with freedom comes the necessity to choose:
with so many topics to pick from, how do you select which research field to devote yourself to? Once this question has been posed, a number of other ones immediately rise to the surface.

  • Do I choose a research direction which is hot right now or one that has been a long-standing unsolved problem?
  • Should I select a topic which is attracting much interest in my own university/country or one where the leading research groups belong to other countries?
  • Is it better to choose a research area that will more easily generate funding from grants or one which I personally find more interesting even if funding will be more difficult?

Not an easy task. I’d say it is quite the balancing act, frankly, because you have at least three aspects to consider.

research-choice-yangFirst of all, you probably want to do research on something that you are personally fascinated by. Otherwise, it will be tough to find the motivation over time. Secondly, personal interest alone is not necessarily the only guideline that should be taken into account – it also seems reasonable to consider topics that will lead to a real and useful advance in knowledge.
For instance, I would argue that it is potentially of higher importance to identify materials that become superconducting at higher temperatures than is possible today than it is to compute an analytical expression for the 10th order correction to the energy eigenvalues of the Schrödinger equation for an anharmonic oscillator, even if you happen to be absolutely fascinated by doing perturbation theory. Thirdly, you have to consider what will be best in order build your scientific career. Some research topics are simply much more strategic than others when it comes to your chances of getting funding and applying for grants. To illustrate this point, think of research problems categorized by their risk and their potential gain. Let me give two examples.

Low risk – low gain

Find an exact solution of the Lagrange equations for a classical particle moving in a potential which has no realization in nature and which does not require any new or interesting mathematical techniques.

High risk – high gain
Develop a model for the normal-state of the high-Tc superconducting cuprates and the underlying microscopic mechanism that generates superconductivity. Many would argue that this
is one of the most important unsolved problems in condensed matter physics. Several brilliant minds have dedicated themselves to this topic over the last 30 years, yet a solution
remains elusive. Certainly a very high risk problem, as a solution is not guaranteed by any means – but the potential gain is equally high, no doubt worthy of a Nobel prize in Physics.

What should you go for then? Well, it seems clear to me that the research field you devote yourself to should have a potentially high gain in order for it to be worthwhile. A high risk
associated with it could make it more suitable for the most prestigious grants such as ERC funding, although it still has to be realistic.

So there you have it – ideally, you should then pick something that you find very interesting, something which will clearly move the research front forward and contribute to an expansion
of useful knowledge compared to what was known previously, and something that will put you in a good position to apply for research funding and grants. If you can find something
matching all these criteria, you have an excellent starting point.

Another aspect that will influence what kind of research direction you choose is which career stage you are in. As a masterstudent, the emphasis is on learning new physics and techniques,
and so a low risk – low gain project is perfectly viable. Proceeding with a Ph.D degree, the risk taking has to be higher since you are now supposed to make a real contribution to the
research community and so it is no longer a good idea to play things completely safe. You get the idea: the importance of moving toward high risk – high gain projects increases as you
continue along your career trajectory.

Some food for thought, hopefully. Stepping outside of the comfort zone and embarking on a research journey which you don’t yet know the outcome of can be scary, but the reward can make it
very worthwhile. And as with many other things in life, the journey itself will be very rewarding in itself.


“When I grow up, I want to …”
  8 August, 2014


If you ask a child “What do you want to do be when you grow up?”, I’m willing to place a fairly generous sum of money on that “Professor” will not be one of the most common answers you’ll get. After all, it is difficult to compete with cool things like astronauts, princesses, and firemen.



But somewhere along the road perspectives change, and perhaps you are one of those that are currently pondering whether or not you should pursue an academic career after completing your Masters- or PhD- degree. What can you expect when taking this road? And how do you make an academic career, anyway?

A fork in the road
Our journey begins at the crossroad encountered at the end of your Masters degree. What now – do you apply for a PhD position or do you go for an industrial job, whether it is in the context of cellphones, oil, or IT-development? A PhD position normally has a duration of 3-4 years in Norway and thus landing a permanent job in a company like Statoil undeniably is more of a safe bet. Moreover, you’ll likely get paid more money there.



A unique opportunity
Then why choose a PhD degree? I’ll tell you one thing – if I could make the choice again, I still wouldn’t have taken an industrial job even if it paid twice as much as a PhD position. Heck, I wouldn’t have taken it if it paid three times as … weeell, maybe I shouldn’t be too hasty …

The point is that obtaining your PhD degree is a completely unique process and cannot be compared to most of other jobs that may be relevant for you after having obtained your Masters-degree. Think about it – as a PhD candidate, you will get paid to have the freedom and time to utterly absorb yourself in a topic that fascinates you and learn all there is to know about it. The result? You will become an expert on a national, and possibly international (depending on how well you do), level in your field of research. Doing scientific research is like opening the pages of a book that has never been read before – you are discovering new things and, importantly, get the exciting privilege of sharing these news with the rest of the world. Yes – the rest of the world – your scientific publications will be read by hundreds of other researchers, young and old, all across this globe.

It is important to underline that after you have obtained a PhD degree, you’re still highly attractive on the industrial job market – and probably even more so compared to if you “only” had your Masters-degree. Holding a PhD degree certainly doesn’t hurt your chances of landing a permanent position outside of the academic environment.

CO2_Solrun-Johanne-Vevelstad_Foto_Per_Henning100% of your time on your research
But what if your thirst for knowledge does not end after your PhD degree – what if the answer to the question “What do you want to be when you grow up?” actually is starting to look alarmingly much like “Professor”? The next step in your pursuit of an academic career would be to enter a so-called postdoctoral (postdoc for short) position. At this point, you will be able to work much more independently as a researcher than you were able to do at the beginning of your PhD studies and it is likely that you will produce some of your finest research work during this stage of your career. You will not have any mandatory courses to attend or lectures to give – you can devote 100% of your focus to research. Trust me, this is something you will miss later on when administrative duties as a lecturer or professor become more time-consuming, leaving less opportunity for sitting down on your own and being creative. Don’t worry, there are up-sides as well later on and I’ll get back to those.

The postdoc stage is quite critical in your career. It’s basically do-or-die: now is the time to show that you have what it takes in terms of being able to come up with new ideas and produce interesting and relevant research, ultimately proving that you are worthy of a permanent position at the university. It is also a stage which seems to scare many graduated PhD candidates – in my experience, very few of the young men and women that obtain their PhD degrees at the Department of Physics where I belong choose to continue down the academic track. There are probably a few reasons for this. One is that postdoc positions are typically short, temporary positions ranging from 1-3 years in duration. That doesn’t offer much stability, which may be an important factor for you if you have or are about to establish a family. Moreover, it is strongly encouraged to do your postdoctoral work somewhere else than you did your PhD work, simply because you get exposed to different research environments and get to acquire new expertise. This can pose a practical obstacle. However, that does not mean that it is impossible to make it if you stay at the same institute as a postdoc due to e.g. family reasons, which I personally did. With that said, given that you have the opportunity to do so, I would encourage you to go abroad – meet new people, see new places, and learn new things that will allow you to develop faster scientifically than if you stayed at your alma mater.



A versatile job
If you work hard in a persistent manner, you will obtain qualifications that allow you to apply for a permanent position at a university: associate professor (førsteamanuensis) or professor. I’m not going to tell you that it is easy to get such a job – but I will tell you that it is worth all the blood and sweat that you need to put into getting it. One thing to note straight away is that it is a really diverse job, in contrast to what many seem to think – you get to teach, do research, supervise younger promising researchers, lead large international projects, and be a spokesperson for your particular field of research and science in general (for instance by writing blog-entries like this). It tests you in many ways, both intellectually and on a personal level – you shouldn’t think of professors as solemn, gray figures sitting in their offices and only peeking out once in a while – it is a truly dynamical profession which requires a lot of interaction with both colleagues and students. To witness your PhD candidate develop from a rookie learning the ropes during his or her first fumbling year into a solid researcher that will turn the tables around and starting teaching you things in the final year is an incredible experience.

Obviously, I cannot hope to encompass all aspects of the academic path in this blog-entry, but perhaps you have a better idea of what to expect if you should choose to pursue this career. It’s not an easy road – but hey, it usually isn’t if something is worthwhile.


What is a theoretical physicist?
  5 May, 2014



Thanks to the unstoppable Sheldon Cooper and the rest of the crew in the popular sitcom “The Big Bang Theory”, the world has been granted a peek at what life is like for young physicists – both on and off campus. Solving complicated equations day and night, with several whiteboards always at hand in their apartment, spending their sparetime watching Firefly with extra commentaries, and pulling all-nighters battling orcs in World of Warcraft – yes, the Big Bang Theory physicists fully embrace the nerd within. But how accurate is the presented picture when comparing to everyday life for a physicist at, say, NTNU?

Not far from the truth
I suppose the answer will depend on who you ask, but surprisingly much is true! Now, not all theoretical physicists have a special shelf-spot for a limited edition Batman belt-buckle, but I think it is fair to say that the majority of us do embrace the nerd within when it comes to our passion for physics. A theoretical physicist is a curious being – he or she is driven by a desire to explore, understand and explain the unknown. Imagine that you are able to discover an equation which describes a physical phenomenon and that you are the first one to ever write down this equation. This is what theoretical physicists do! They unlock the secrets of nature and expose them both in terms of a mathematical language and in terms of how to interpret the equations physically.

Social skills needed
Some people may think that physicists are asocial, awkward beings incapable of interacting socially with much success. This is very far from the truth. Being a physicist often entails very much interactions with other researchers, especially from other parts of the world. This task comes with responsibility: it is important to grasp at least the basic elements of the culture of the researcher you are communicating with in order to treat them with respect and understanding. I have collaborators both in the United States and in Japan, and I can assure you that these cultures are very different. In turn, this influences the way that I communicate and express myself with my collaborators. Being a theoretical physicist allows you to get to know completely different parts of the world and learn about what these cultures value and cherish – interestingly, you also get to know yourself better in this process.

Curious about how the world works
The life of a theoretical physicist is very exciting. You find yourself day after day at the frontier of what we know about nature and how it works, and you are a part of pushing that frontier further ahead with your contribution. If you are a curious human being who enjoys math and wants to understand how the world works, I can warmly recommend exploring the path of theoretical physics – whether you own the complete set of Star Trek DVD’s or not.

More information about Theoretical Physics at NTNU